I’ve had my account since 2006 or 2007, yet it's listed as just two years and nine months. I don't want help fixing anything, per se; I'm just curious if anyone knows why this would be? I didn't sign into my account for a while, so is it possible it "reset" when I logged in back in 2012? Not knowing what happened is driving me nuts. ;p

You could try filing a ticket and asking a user admin to look into it.

http://subeta.net/tickets.php

Back in the day, accounts were deleted if they were inactive for too long. Are you sure you didn't have to recreate your account when you came back in 2012?

I don’t remember recreating my account (I even have the same pets), but I must have? I only remember logging in and seeing a few unexplained changes (my profile looked different, some of my items were missing, etc.), yet thinking nothing of it till now. It’s all very mysterious!

Yes users who's accounts were cleaned from the system had to be made again. These days though when an account hits inactivity it no longer deletes but DOES allow names to be snagged. This way items you saved for, achievements earned ect ect aren't lost, just names and you get free renames if that happens.

But your case sounds very strange and I second the notion of making a ticket to have someone recheck what happened to your account timer.