Det förklaras aldrig.
Från Infospheres sida på tidskoden:
It is interesting to note that it has yet to be truly explained where the time code comes from or how it ended up on Fry's butt in the first place. The code was put on the frozen Fry's butt by Bender, using a flap of skin from Lars, but it only existed on Lars' butt because he is a paradox time copy of Fry. This is an example of the bootstrap paradox.
Den ursprungliga lagen av tidskoden som placeras på Fry visas aldrig och förmodligen raderades från tidslinjen helt.