I have a Bowen tuned SBH that came with all the paperwork for the work performed (over multiple years actually, as the prior owner sent it back for additional work twice).
Work included DX front sight, Bowen rear, turn barrel back/remove markings, fix endshake, hone throats, action work, freewheel ratchet, and idk what else off the top of my head. It's basically as far as you can take a gun without replacing factory parts.
The gun isn't marked. I think he only marks custom cylinders and full builds/caliber conversions. Mine started and ended as a 44 mag with factory barrel. It has the smoothest action of any gun I own, and that included fast draw guns by Munden.
I'm sure your gun was Bowen tuned, so no worries there. The letter stating what work was done might help resale or help you get more money, but don't feel like you should need it to reassure yourself.
Congrats on a nice purchase!