I think it is highly unlikely that anyone would be able to fake a GA comic book. Heck, Marvel and DC have had enough trouble converting them into a presentable form for Archives or Masterworks that they resorted to lower quality scanning or redrawing to create a presentable facsimile -- and those are readily distinguishable from the originals by a mere eyeball test, without even doing any of the sorts of scientific evaluation that might be used to assess whether a painting is a fake.
And its not like you can just pass off a counterfiet Action 1 on a street corner. Realistically, you are going to have to fool sophisticated collectors, auctioneers, and, probably, third party graders. I wouldn't lose any sleep over this one.
I also don't think that the very slight risk would create much more interest in a comic's "provenance" than now exists. Seems like many collectors and dealers are already under suspicion for shady practices at one point or another -- whether thats restoring books, passing off restored books as unrestored, overly generous grading, or even, I've read, forging the identifying marks of certain pedigrees on to non-pedigree books. So provenance ultimately seems a negative concern, not a positive one, if it can be discerned at all. Why would anyone care about provenance when CGC certification rules the market?