Phew... Great news... I guess that now you can immediately recognize a Pre-AI, AI, AI-S lens !!!! On the second hand market there are quite a few Pre-AI that were AI'sed, those can be interesting lenses to get, specially if you also have an "older" film camera (or will try at some time in the future).
There are many shops that will do the proper filing job, but it's harder nowadays to get the proper replacement part for the small aperture numbers on the lens mount, unless cannibalizing some broken equivalent lenses ( don't throw those lenses, keep the parts)!