Or just paint the new hydro white like we do for steel cylinders so it grabs the tank monkeys attention. Seriously, what tank monkey looks for anything but the most recent hydro? Nobody got time for inspecting old hydro marks when they have 30 tanks to fill. 90% of FSO's don't scrutinize a hydro stamp anyway, they just look for a number larger than "19" to the right of the RIN #.At this point much of the surface disturbance is from the paint being stamped. If one wants to do anything, strip the paint off and repaint it. A couple of coats of paint will likely fill in the marks such that they will be hard to see.
I've visually inspected older steels with 4 or 5 hydro stamps on them. Some of the older requalification stamps I couldn't read they were so light. All PSI wants to see on their form is "first hydro date" and "last hydro date".
If a cylinder was hydro'd last week and passed, then it's a good cylinder as far as REE goes.