[Turk]

Good luck getting a SB 100 number in December.

I predict the numbers will be all gone by the end of January.
60 days plus is what you get for registration to drive your car while you comply with the CHP and BAR portions of the ordeal.

If your construction, or appointments at CHP etc. are delayed they are pretty good about issuing another extension and another,

I was given three last year, mostly because I was ready but DMV wasn't.

It is true you can take the rest of the year to finish your construction or your registration.Since your temporary expires in 60 plus days, you just can't drive it!
out of it.

jdog,
Once they issue 500 they are finished. They don't care if you finish your car or make a planter out of it. There won't be #501 or #502, because the guy who had 305 left the state or died and his car is never going to be registered.