I read through the wikipedia pages, but couldn't find any reference. Why do they start at 92? It's 50 years later, not 40.
The way that I understand it now is that the creator wanted to set Season 5 with the 50 year timeskip represented as the conclusion of Season 5 as an unstated CII.
It's already established that 50 years have already passed but here's my theory. The season 4 episode began as LII (52), and season 5 began as XCII (92). When you as an audience finish watching XCII, you are technically finished with XCII and are at the start of XCIII (93) and so on.
With this in mind, and the fact that Season 5 is only 10 episodes, the last episode of the season will be represented as CI (101). This represents the beginning to the end. Once you reach the end of CI, you have reached the beginning of CII, hence, the 50 years are represented.
The actual time skip in the story is somewhat irrelevant to each episode's roman numerals, but not completely.
I guess, if you assume that the first 52 episodes took place in 10 years' time; plus the 40 years, as Jack says it has been 50 years, then that gives us 92. I think, Genndy has said somewhere that the episode title is just to show the passage of time. So, it's not important what the number is, unless it is a mystery that will be revealed later.
If this season did have 13 episodes, like all of the others, the final episode would have been CIV. 104 is 13*8, implying that there are three lost seasons that would have gone after season 4 and before season 5. This just means that they wanted the starting number for the final season to match what would otherwise have been a starting number for a regular season. They could have chosen to skip over 3 seasons in particular for any reason.
Personally, I'm still hoping that this means that episode CI will be massive, effectively the length of 4 regular episodes in order to keep with the 13 episodes per season pattern. A guy can dream.