Joe, don't worry about dragging a post out, forums are for learning & many others not yet knowing what all the hell they are doing will read the newer posts & benefit. Sanding through is an all too common thing that has to be dealt with & has been posted about in various threads throughout the years, but would take a while to find.
Yes, this is no longer a rattle can post, not everyone reads everything in a thread completely. many threads change direction from title.
Much info here is posted as best way possible for high end restoration, good & better , not 100% best & what can get by with get done every day.
While having epoxy touching every spec of steel is best, particularly in rust prone areas, some getting away with small slivers is common even among really good painters for various reasons. Touch up of epoxy in said areas is best & epoxy between other product coats with proper time windows is just fine. Light touch up on even tiny spots is my preference, large spots are my firm rule. I've had numerous tiny sand throughs I've gotten away with YEARS later, no evidence. Gotten away with is the term here.
Pull up the pdf file on evercoat g-2 featherfill. They recommend epoxy on bare steel, but back off saying less than quarter size sand through is acceptable.
So, your choice here. You're already going beyond what the average Joe is doing , don't stress too much.
If your sand throughs have been exposed for more than a few hours, give em a light sandpaper swipe before any respraying. Clean steel or aluminum is more important ahead of absolute best coating procedure. I'd consider that a rule.
Joe in Fl.