"only things used for final inspection need to be calibrated"
Correct, at my previous employer they were verifying all of the fitter's and welder's tools....I found that to be a complete waste of energy and time. I cut out all of that nonsense and only verified the inspection tools that would actually be accepting or rejecting the work for in-process or final inspections in both the fab and paint shops.
Jordan there are also endorsements that the fabricator can add on to their AISC certifications...ie the sophisticated paint endorsement- which has several categories..ie enclosed, covered and open/exposed shop
If you want to help fab shops with this QMS get familiar with SSPC and NACE to get a good handle on surface prep, coating application/curing and inspection. Without some core knowledge of these if may be tough to help them cover their bases in that aspect.
Keep asking questions, I'm sure many of us here can help you get your feet wet writing quality manuals for companies. It sure helps if you understand how a particular shop operates to be able to help them with their manual.