No worries; that makes sense.
FWIW, for my Ruger 77/44 & its 5/8"x24 threading; the bbl OD at 16.5" was also an insufficient 0.635".
The solution for that situation was to do the bbl threading extra-long at the muzzle; thread on a thread protector all the way down to create a good shoulder (which got faced as well), then turning off the knurling so as to not look /exceedingly/ ugly. Not the most attractive solution by any stretch, but was certainly satisfactory for getting around what would have been a marginal/problematic situation.