I know they live in apartments 4A and 4B, but in the episode "The Vegas Renormalization" (season 2 episode 21, episode 38 overall), when Sheldon and Penny walk up the stairs they only walk up three flights of stairs. So the question more is:
- are there other instances where characters are seen walking up four (or perhaps more) flights?
- have the creators/actors ever commented on this (it's really minor, so I would be a little surprised if they have)?
- is there anything else to say about this?
- can we actually tell if which floor is skipped in that sequence?
After two of the flights we can see the sign on 3A, so the missing floor most be either 1 or 2. After the first flight the sign on the B apartment comes into view (but it's not readable to me), there's also a little white board with some text on that door, maybe we see that on other occasions that allow us to tell what floor that is?
And another related thing: Do we ever hear how many floors are in the building? The characters are seen on the roof (at least twice - for the expiriment with firing a laser at the moon, and for Howard and Bernadettes wedding) and the roof is referenced in "The Nerdvana Annihilation" (when then guys block the stairs moving the time machine up, and Penny has to go via the roof and the neighbor building to get to work). But I don't remember hearing how many floors are in the building.