Originally Posted by base2

On mobile it's hard to tell. Really, it depends on whether or not you actually got into the fibers. You would be able to tell. If it's unidirectional there will be a sheen one way or the other where they all look in a line. Like how the sides of your fork look under the clear coat, but duller and only when the light catches it right. If it's a weave, then you would see the texture as you started going through the resin into the fabric. It looks like you would expect if you dropped super glue on a table cloth and tried to sand it out.

In making carbon parts there is a caul side and a plate side. It is common practice to add a sacrificial layer of fiberglass mat in areas where abrasion is expected in service. Indeed, in repairs, we add 1 extra layer above the repair just for good measure.

If the guy you took it to saw it in person, and claims he can not see any fibers. Good. The sacrificial layer did it's job.

Carbon bike forks usually have aluminum crowns any way. There's no telling where the carbon blade actually starts. There's a reasonable chance you abraded the transition filler. Theres no telling what that filler is. It could be Bondo for all any one knows! So no harm, no foul.

Having said all that, I would defer to good sense and regular close inspections. Even then if concerned, 'derate" the part until a replacement is found. I have a CX fork that has been abraded in several places near the drop out from a sloppy bike rack placement. I inspect it often during regular maintenance. 5000 miles no issues, but the disc brake side is purposefully extra tough, & theres no fibers visible. YMMV