Hmmm,
I've never noticed a bow shift much after having the first few arrows through it, but maybe that's I'd still be adjusting it and fettling/finishing etc for a while.
By the time I say it's finished it's probably had a couple of dozen and plenty of exercising.
Maybe a suplementary question is, how far do you draw test a bow to?
If it's for 28" draw I'd take it to 29" for most designs, for a self Yew longbow I know it will go further, but wouldn't take it there untill it had been thoroughly broken it.
Del