What we ‘hypothesized’ about the ‘full’ status is that for a while they used one server from NA (and likely one on EU) that was their max server. For a long time (and maybe even now) BG was that server. No matter how many players left, they stayed full. The hypothesis was as BG dropped? Other servers became full based on that benchmark. It drove players to less populated servers. Over time (and we are talking years) BG started to open again, but they only kept them open for hours at a time then likely manually closed them again. Gradually, that ‘full threshold’ dropped. So…. Now we have a much lower ‘full threshold’. Which also means, some servers that were ‘open’ and a certain population/play hours, would now be full.
But play hours has always been their stated process.
As to all of the specifics, they won’t release it. Period. So, to some extent, we are speculating. But it does make me laugh when people keep asking Anet to tell us…. They have NOTHING to gain by posting the actual activity numbers.