Couple things. The 3E magazine (Dungeon 110, “D110”) says that the “current” date is 20 years into the 194th King’s Age. The original campaign setting states that the “current” year is the 26th year of the 190th king’s age. That’s 314 year’s difference. Referred to in D110 as “about 300 years ago.”
Dragon’s Crown took place in the 30th year of the 190th king’s age (according to beyond the prism pentad, although according to dragon’s crown itself, all 5 adventures in that “path” occurred in the same year of Tyr’s liberation).
In D110 in the Nibenay section, the élan are said to have appeared “about 300 years ago” when the Order’s leadership was wiped out. It seems to be a pretty obvious reference to the Dragon’s Crown path.
In Dragon 319 it doesn’t say that the élan were created 100 years ago, it says that some élan still owe allegiance to the Order even though the Order was factionalized and driven underground after a failed plot 100 years ago, and says that Elan enclaves are a recent thing, so no KNOWN Elans have been élan for more than 25 years (not counting their prior lives as humans).
My take on this? They were created around the time of the original setting by one of the splintered groups of the Order. ~200 years later the Order did something ELSE on the order (haha) of their Psionatrix plot, and were AGAIN splintered. More recently (within the past 3 decades), the élan themselves (“a special élan council”) have begun making more of their kind (of the youthful red-haired variety), INDEPENDENT of the Order as a whole, which is why the typical “known” élan that people come across have all been élan for less than 25 years.
tl;dr the élan were originally created shortly after dragon’s crown. At some point 200-ish years later the Order does something else and gets all but wiped out. About 270 years after Dragon’s Crown the élan themselves basically go rampant (in the AI sense) and begin “procreating” on their own terms, rather than according to the wishes of the (now all-but defunct) Order.