I think that the copyright of GLaDOS and the calendars were meant to show that Aperture Science had been around longer than Black Mesa. I'll have to double check my facts but I was lead to believe that the timeline of Portal matches up somewhat with the happenings of Half-Life 1. The next episodes of Half-Life 2, which I already eagerly await, are bound to explain much more about the relation of Aperture and Black Mesa.
Oh, another thing that made me think it was 80s was the radios. Very late 70isk... Just another thought...
Supposedly, according to my brother, he found some kind of timeline on aperature science that details their career.
I thought it was funny, in their early years, supposedly, they designed revolutionary curtain rods among other silly things.
lol, i'm pretty sure i am
EDIT
I'm pretty sure you are..
Holy crap. Ok, so the portal technology was created and tested around 1981-1985
I think that the Borealis is carrying a large-scale version of the portal technology, which the Combine want because they don't have anything like it (as alluded to by Alyx and Mossman in HL2), and having it would make transport between their worlds easier and faster, not to mention "cheaper" (since they had to blow up the fucking Citadel to try and open one).