I thought they regained their memories of everything that had happened after they were woken back up? If I'm misremembering that does change things some I suppose.
I only remember scattered bits of the original dub but I think at most they had scattered flashes similar to Ranma at first. They only got everything back when they transformed into Senshi again.
What happened was that after the reset everyone went back to civilian life. Ranma and Genma would have moved on before the events transpired that restored the Inner Senshi, which went something like this:
Dregs of the Dark Kingdom pop up, Luna restores Usagi's memories, Usagi runs it alone (successfully) for a time. [Ranma and Genma leave their Juuban campsite, no forwarding address left behind; I got the impression reading the flashbacks that Genma actually acquiesced to stay put due to the need for Ranma to help out, but without that pressure, they moved on]
New enemy pops up, Usagi does OK until ... she basically ends up in a fight to heavy for one fighter to take on. Circumstances happened that resulted in the four Inners being present to observe in person Usagi fighting and on the way to losing. While watching the actual fight, they start to have impressions they should be doing something, this is familiar somehow, what is going on why do I feel I know these other girls beside me and Sailor Moon as well... ?
Luna spots them, mutters a quick apology to Usagi for going against her desire to let the girls have their civilian lives, and pops their memories free.
Inners transform, save the day, big reunion.
BUT RANMA WAS GONE AND LEFT NO CLUE AS TO WHERE HE WENT. Even if Usagi would have wanted to bring Ranma back into their group (not a safe bet considering how much she was trying to make sure the other Inners got to stay out of things) she couldn't without a way to find him.
It's a difficult thing to consider these days, but at the actual time setting these stories originally landed in (early 90's)
social media wasn't even a single line of code on the computer screen.
No easy way for the insanity that is Nerima to even enter public consciousness as a spring of internet rumors about how crazy this place is, heavens, martial artists fights all over the place, a pair of siblings (one redhead girl, one black haired boy) being node points of the whole mess...
... actually a line in the chapter makes me think that Luna and Artemis managed to heal the Neko-ken-induced fear, otherwise Ranma would never have hung around, and that cure got wiped like everything else.
Why wouldn't Setsuna have mentioned it when she rejoins them later? Senshi can't be easy to track. If there were an easy method they stood out with they could have been tracked down by the Dark Kingdom or any of their other enemies over the years. Without a clue to go on, no social media internet craze to produce something the Mercury Computer could latch on to, Ranma is effectively completely out of the picture.
Another poster commented on the memory block finally starting to give way. Which given the sheer amount of magic and power being thrown around at Jusendo definitely sounds like it might have been able to tweak something loose.
And all you need to start a landslide is a single pebble shifting in just the right way to start everything else into motion.
