okay now one thing that i'm thinking is that 1999 is The pivotal, important year... because it's the year of the infestation outbreak, right? when we got introduced to it i thought "yeah of course, the temporal ground zero for the technocyte plague"
it's at least something that isn't common knowledge, or doesn't have a foothold in the world yet. the biggest thing spoken about over the PAs is Y2K and new year's seems to just go off like new year's, and that kind of implies to me that arthur and aoi are in a place similar to hayden in darkSector - they're in the middle of a mission to stop the outbreak before it spreads, and albrecht is an important part of that.
of course with the added element of eternalism and accompanying themes of time travel, a theory i could throw at the wall to see if it sticks is, like. idk the infestation was brought back to 1999 from the future due to some orokin meddling? darksector isn't close-canon but the remark that the first instance of a warframe-like presence would have happened far enough in the past that it had no conventional bearing on the present day plot... yk, maybe like the turn of the 21st century...