23andMe wouldn't be able to report it like that. As far as I can tell, they only can handle binary results. So if the allele isn't "C" they seem to assume it must be "T", for example. For nearly all of the SNPs which they test, this isn't a problem, because the possible results really are that binary. They simply don't test SNPs which have 3 or 4 possible results at all, which is why there's almost no HLA genetic data available from 23andME.However, if it were, say, AT, that would have to be a mutation, since the inverse (TA) is not a suggested base pair?
Hence 23andMe will only report the two alleles which they list as options. It's possible that there are more options in a few cases, but I've only seen a strong indication of that in the mitochondrial DNA, where they get no-calls at the same place for everyone with a certain maternal haplogroup, etc. But that isn't happening at all on CBS, or the vast majority of other genes.