The mutations which produced the ABO alleles are ancient, but the A and B genes were in scarce supply prior to 25-50 thousand years ago. Their gradual increase in number was a result of the forces brought about by neolithic changes including the greater lethality of pandemics and communicable diseases which worked against type O.

This was simplified somewhat in ER, but in fact is true. Should you wish, you can read someone like AE Mourant for further information.

The shroud could theoretically be Christ's and AB as well. ER only makes the point that AB are not found in significant numbers of grave exhumations until the Langobard Era (ca 900AD). However that doesn't mean that they were not found in insignificant numbers prior to that.

However, at least one Egyptian pharoah has been typed as AB, indicating that admixing of A and B genes was already occurring by 3,000 BCE. The influx of the conquering Hyskos (a semitic tribe) into Egypt and their mixing with indigenous Indo-European strains would have produced some AB -especially at the upper rungs of Egyptian society that resulted from intermarriage.

By the way, I'm not certain that one can be 'very wrong.'