From what I've read the bolts have most likely "set" after sitting for as little as a few hours in which case it is quite possible you will read a much higher torque than actual without backing the fastener out a bit. Besides, there's no harm to be had from backing off each of the bolts a quarter turn before torquing them to a higher value.
EDIT: I might as well add that while you're torquing a fastener, if it starts to feel as if it's not rotating smoothly or is stuttering or popping you need to back it off to relieve the seizure/set and ten continue. The bolt *should* rotate smoothly up to the desired torque or you are likely to be getting a false reading. Naturally, when/if a fastener will set depends on many factors; It might not happen at all, but if accuracy is required, well...
EDIT: I might as well add that while you're torquing a fastener, if it starts to feel as if it's not rotating smoothly or is stuttering or popping you need to back it off to relieve the seizure/set and ten continue. The bolt *should* rotate smoothly up to the desired torque or you are likely to be getting a false reading. Naturally, when/if a fastener will set depends on many factors; It might not happen at all, but if accuracy is required, well...
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