Clerical error? Dunno. I think it is a dumb way of documenting. So here's what I think happened: 1. Someone sent the coin to NGC and filled out the form "item 1: 1815/2 50C." 2. NGC could not read the date, so they determined they could not holder the coin. 3. FOR RECORDING PURPOSES, NGC labels "item #1 1815/2" as date not readable. BUT since they leave the date of item number 1 on the sticker, the seller can now sort of claim that it's a 1815/2. Now, first of all, NGC should have easily been able to tell that it was an E/A reverse (and thereby an 1814)... such a bold and easily identifiable die marker. Second of all, by leaving "1815/2" on the label, they are enabling the owner of the coin to still perpetuate the fantasy that it COULD BE a 1815/2.
My only contention is, just how many "clerical errors" does it take to lose faith in the TPG's reliability? They're either blowing the attribution or the quality control process, at a rate unacceptable in any other manufacturing process. Their whole claim to viability is "take us at our word."