But to be fair, this mixed does lend itself very well to a nice "everyone knows everyone" mindset or headcanon where all the "alumni" know or at least know of each other. (I haven't followed any of the shows closely since early Zeo, and I've been holding off getting into the comics, so idk if that's also been played with there.)
Yeah, when later seasons started doing more team-up episodes between previous and current ranger teams, the show began to grow a sense of different teams coming to know more about each other until, over time, this big network of past rangers all knowing each other pretty much blossomed into what it is today.
The 10th anniversary episode in Wild Force, "Forever Red", showed that most of the ten Red Rangers who all teamed up together in that special already knew each other by the time of that episode, with only the newest Red Ranger, Cole, meeting most of them for the first time ever in that episode.
By the time of the 21st season, Super Megaforce, it's established that there's a whole Ranger Database that chronicles all of the history and exploits of previous ranger teams from MMPR season 1 onward, and which would go on to be shared with other ranger teams in later seasons to each apprised of the other teams.
Also in Super Megaforce, the final episode had the big Legendary Battle with every past ranger coming to help the current team fight their last big battle of the season, forming a large Power Ranger army. Those among them who removed their helmets before the battle let the newest team know that the older rangers were all aware of the new team's efforts and commended them for it, pretty much making it clear that all of the past rangers had by now come to be very familiar with each other offscreen.
This extended familiarity carried over into the 25th anniversary episode in Super Ninja Steel, "Dimensions in Danger", where another group of ten past rangers from various different teams across the Zordon Era, the Post-Zordon Era, the Disney Era, and the Neo-Saban Era, were all gathered together and shown to already know each other beforehand, including rangers from different universes (specifically, RPM and Dino Charge/Dino Super Change took place in separate universes from the main one), having visited to the main universe via portal technology.
I have no idea how the Dino powers are back (MMPR's run destroyed and rebooted things a number of times, literally dusting the last batch of Power Coins at the end). But I figure with Adam having shown up once or twice in earlier series and the Red and Green Rangers showing up a while back as well that this is something that was addressed long ago. Or at least handwaved away. (Forgive my lack of lore knowledge.)
Yeah, the restoration of the MMPR powers has been something of an enigma, but by now it's no longer really questioned anymore since there's been several reappearances of MMPR rangers in the years since.
The original Power Coins were shorted out when Rita's brother Rito destroyed the Thunder Megazord and White Tigerzord at the beginning of MMPR Season 3, so the Rangers got new Ninja Power Coins from Ninjor. But then Goldar destroyed those coins during the Mighty Morphin Alien Rangers mini-series that bridged the gap between MMPR Season 3 and Zeo.
During In Space, Adam returned for one episode in which he showed that he still had his original morpher with the damaged Mastodon coin in it, and tried to morph into the MMPR Black Ranger with it despite Alpha telling him that doing so might kill him. He succeeded in morphing, but in an unstable state that could barely be sustained and severely hurt him. Fortunately, he survived the ordeal.
In the aforementioned "Forever Red" episode, Jason returned as the representative of MMPR and morphed into the original Red Ranger form using the Tyrannosaurus coin. How he got his powers back (especially after having transferred them to Rocky) was never explained, but most just assumed that Rocky simply gave Jason back the morpher at some previous point offscreen, and that either the original coin was somehow repaired or a new one was made.
When Adam came back again for the 15th anniversary episode in Operation Overdrive, "Once A Ranger (Parts 1-2)", he again morphed into the MMPR Black Ranger using the Mastodon coin, but it was actually explained in that episode that Adam's powers (as well as those of the four other past rangers who also came back for this two-parter) were magically restored by the powers of a magical being known as the Sentinel Knight, who was a recurring character during that season.
By the time of the aforementioned Super Megaforce finale, every single morphing power of every single previous ranger team was working again. While no explanation was given, by this point, enough time had past in the franchise's history that it was believable for every previous ranger team who had ever lost their powers to now have them back again.
But in the aforementioned "Dimensions in Danger", Tommy was one of the returning faces and revealed that he was in the possession of a special morpher called the Master Morpher, which enabled him to access the powers of nearly every single morphing power he's ever had. In that episode, he demonstrated the Master Morpher's ability to let him morph into MMPR Green, MMPR While, Zeo Red, and Dino Thunder Black (he didn't morph into Turbo Red, but the comics revealed that the Master Morpher has that form too). No explanation was given for where the Master Morpher came from or how Tommy got it, but by that point, there had been several seasons of Ranger teams having manmade morphers that the Master Morpher's origins didn't feel as needing to be explained as it would have felt had it been introduced many seasons earlier. Plus, by then, we were in a post-Super Megaforce world, so old powers coming back with no explanation was pretty much old news by that point.
I actually wanted more Bulk and Skull. They're lifers and iirc fairly cool dudes in general. Genuinely thought at first that the person falling through the sign was Skull, and hoped they'd pop in at the end at the Juice Bar (which is just as 90s as ever).
I was okay with the lack of Bulk and Skull since, even though it was all the way back in 2011-2012, Bulk previously returned as a series regular for all of Samurai and Super Samurai, and Skull reunited with him for a guest appearance in the final episode of the latter. And in that final episode, Skull was revealed to be super rich, with a limousine and fancy clothes and everything. Taking this special into account, Maybe Skull is the head of a successful sandwich company and he finally brought Bulk in as his business partner (though, why he and Bulk weren't already business partners during Samurai raises some more questions, but still).
And before that, both had also returned for a single scene in "Forever Red".
To be honest, when trailers first broke I was a bit surprised at Trini's death being written into the plot as an in-the-line-of-duty death. All these years I'd figured it might be in better taste to just have it be a natural death off-duty, living her civilian life post-peace conference, maybe after having started a family but not while/from fighting Rita. I'm still not sure I like this direction any better, but I do appreciate how it was handled.
I don't disagree. I had originally wished that, if they were going to say she died, that it would have been something that happened years ago offscreen and just leave it at that. Rita killing her in cold-blood initially felt kinda harsh, but I agree that they handled the aftermath of her death very well.