This community is at least a little different from the Pathfinder crowd (I say that with a foot in both camps). As I said above, I think I know what the OP is talking about, but a bit more explanation would help SOME people here. There is no official mechanism to pass XP down through the generations in AToW, but I think there could be. Done right, it would be AWESOME! 
Not really confined to advanture paths; modern APs are just a good measuring stick for time, since they are a set length format (as opposed to other campaigns, i.e. ones I wrote myself or converted AD&D ones) and the one in question had a uniquely-defined start date.
I mean, the longest running party we had - which was in Rolemaster, system of choice before 3.0.3.5/PF1 came along* - (which, granted was run on day quests, which happen quarterly and usually not the same party in a row, so maybe one or two a year and thus not a weekly evening campaign) lasted about, oh,
22-24 years. And ended when I specifically did a double-length capstone adventure for my 40th birthday party in late 2019. A party which I choose to officially retire, since we getting older and the characters were stupidly power-bloated (the final boss was a 60th level great time drake ninja lich with precursoer technology shields...
For a 12th-level party).
Related image. Disturbingly prophetically, since we lost one over lockdown, and it was one of the younger players, too (36 is no age to go).
I can only estimate the duration, since the first quests predated me having a PC, and thus I can't check the exact date of the files of the first quest I have on computer because has been through pretty much every PC, and I am only certain that, unlike some of the supplementary weapon lists it wasn't written on the Atari ST first was because that quest (quest 02) was written for my special double-length advanture for my 18th birthday (late '97), and that was a crossover of two already existant parties.
My estimation puts it around sometime 1994-1996 start... And I only know that because one of the characters first appeared as an NPC in a RM time-travel campaign, which I can tie to 1994 date specifically because of an incident I randomly recorded in my school jotter with the date because of the remarkable incidient the guy who was playing himself killed a 5th level time-lizardman with a cricketball after the entire rest of the party with their advanced sci-fi weaponry entirely failed to hit it. Over the years, this sort of thing became standard for RM, but it was the first time...)
*We did play AD&D a bit in the day, though never quite the same set of rules under each DM. But when 3.0 came out, we never looked back, though. We now (primarily) play 3.Aotrs, because at the point you have 1000+ pages of houserules, you functional have your own edition (admittedly, a fair amount copy-pasted from 3.5 or PF1 and just collated in one place to theorhetically reduced the amount of physical paperwork which would otherwise exceed what wil fit in my 90-litre backpack; but like with the changes from 3.5 from 3.0 and PF1 from 3.5, there are quite a few bits where there's a few changes.) RM still sees some use (well, theorhetically, I haven't written a single quest of my own since lockdown) as it serves some purposes better than 3.Aotrs (for more skill-based, less combat heavy, more explore-y games)
