Not sure how many people are still following this blog, or rather who's still interested on those headcanons + ideas i had in the past...
But Rui's existence goes against ▽ events and i'd like to clarify that i don't think it's a TOTAL RETCON like a ton of people are either celebrating or complaining.
I'd like to give you my own "solution" to keep Maki and Daigo + their group existing in the timeline.
First, the frustrating part about working with ▽ events and them is that there's no information about their respective ages, and we saw them in Uni as well. A friend of mine pointed this out as the biggest problem to use ▽ as it is. You either pick it or 02TB. My research about the said backstory scenes in pt4 led me to discover that... those scenes also are hard to know when they take place.
Not even the ref sheets has a single age or grad to get an approximated age for them, or when those scenes took place. They only state that those two designs are from "Elementary School" and "University" -- but the Elementary grades are not even here!? Unlike the Adv'99 & 02 kids' profiles in their respective series, which listed at least their school grades so you could know they're around their 10s.
But we know the original lore from Adv'99 + 02 -- there were other groups before Taichi & Daisuke's. One of them were depicted in Adv'99 anime and novel -- a group of five kids, and four of them got their partners evolved into the Holy Beasts (according to the Adv'99 novel). This is also used in ▽ pt4, at least. They changed a few details alas, but my point is... Until here it's everything OKAY, right?
The problem starts with the Uni scene and them being Data Bureau agents in 2005. It could mean they're way older than Taichi -- including Rui (who's a leap baby from 1992!) and this would get in conflict with their own Digi-Adventure flashbacks. Many people believed they weren't from the 90s but before the 90s because of that. You could then think they had no relation to the math lore or something, but then the presence of Homeostasis in that cold-opening for pt4 and the digivice model makes things EVEN WORSE to work with.
But like i said, i love both Maki-Daigo and Rui so i want them to co-exist. Hence why i'm believing in a partial retcon in terms of those two's ages. And it's quite recently that we all got more info about the math lore, and more confusing statements in the end...
Maki-Daigo's group is indeed the quintet mentioned in Adv'99 & Novels. They were around Adv!Taichi's age when they went to the DW but possibly the other three in the group were either 2 or 3 years older. Maybe they're like the 02 kids, and weren't chosen exactly in the same year? Possibly the oldies were the other 3 who got mons alongside Menoa (she's the same age as Taichi and got her mon in 97), But Daigo and Maki got their mons in 98, alongside other 7 people...? And their Adventure was indeed in 1998.
Daigo's love confession scene has no calendars or anything to point the year he had confessed his love for her, besides being SNOWING outside -- so it's probably Winter. They're said to be Uni students, so my conclusion is...
... That the Data Bureau possibly recruited them around that time, and they're not even in their 30s in ▽? They might be even 19 years old, and only got high roles in the Data Bureau because of their title as Chosen Children and connection with Homeo + Gennai.
They aren't the first ones, but actually they might be the first group of kids who went to the DW instead.
This is my own solution for the problem. Again, I'd prefer to believe in a soft retcon or changes from the events -- in which said events in the timeline weren't presented as it is to us. Therefore i'd prefer to believe my awful people OTP is still alive and they can meet my sad potato someday.
I'd like to simple just retcon their ages from 1998 adventure and make them be 13-14 years old there, so then you could have them be in their twenties when they were recruited by the Data Bureau...
Anyway, i understand when some peeps say they can't make ▽ work with Adv'99/02/Kizuna/02TB as it was presented to the audience, because it's a hard task orz