Doug,
Sam is right. Your TRE signature is valid immediatly. But the paperwork goes to the issuing authority and it is checked there. So in practice, if the TRE amkes a serious paperwork error, you could get a call in 2 weeks saying your rating is not valid....and it happens.
the system is based on the fact that the TRE is probably a real TRE and he didn't make any mistakes. If you look at the opposite type of system....well it would be hell for us....having to wait until your paperwrok is rubber stamped by 10 departments in your CAA and then you go to the belgrano to collect your license after queueing for half a day!!! I think we have it 'sensible' where it's at....don't knock it
BH