John,
Haynes doesn't talk about this because Haynes is,.... well...ya know.
Yes, stretch bolts do indeed stretch and fail to "shrink" when detorqued. They become useless.
More importantly, ALWAYS use NEW rod bolts and nuts when rebuilding any engine you'd like to see run well and last long. period.
Have you had the rods checked/rebuilt by a competent machinist? If a machinist knows what he's doing, he'll ask for a set of new (if non-stretch) bolts when he assembles your rods for inspection/correction.
Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon