Thank you brother, no worry about limb weakening or the cables or string being stretched or whatever?
If you happened to have shot the crossbow using a chronograph, one would have an idea if there was a difference.
As for string and or string and cable stretch a couple things this depends on: 1)if the crossbow was shot a fair bit before, then the string and cables would already have stretched. 2)If the string and cables were properly built, even if shooting before there should be little to no stretch.
If the string and cables have stretched, it is just a matter of retuning the crossbow. Your manual may give the axle to axle measurement but that is only a guide line. Changing string and or string and cables or tuning, this measurement can change.
Advancing cams to match the manufactures advertised speed or to increase speed in feet per second, taking into consideration using an over weight arrow-point combination, this measurement can change.
If the crossbow stayed in tune, and suppose the limbs did weaken a bit, the crossbow would shoot a bit slower. The limbs should have a safety factor built into them where they can actually go higher than normal shooting.
As an example: a crossbow with 185 pound draw weight limbs, one does not build a bow string with a tensile strength of 185 pound. One would build it 300 or higher for the fact when the crossbow is shot, until the bowstring stabilizes there is going to be a lot of vibration. If string stops are used with next to no gap, when the string hits, the limbs still carry forward motion until they come to rest. One would want a built in safety factor.
Using my Barnett Ghost 410 as an example, the manual suggests 20" axle to axle when the crossbow is uncocked. My Ghost is modified with higher quality parts etc. and tuned to shoot well over Barnett's advertised speed. The axle to axle measurement averages 19 3/8".
The manufacture advertised the Ghost to shoot a 20" Barnett Custom Head Hunter 400 grain arrow-point combination at 410 feet per second. The Ghost is shooting a 20" Carbon Express Pile Driver 450 grain arrow-point combination averaging 421 to 423 feet per second. This is the the equivalent of shooting the 400 grain arrow-point combination at 436 to 438 feet per second.
All the best.