Have you checked http://www.ultimacollectors.info/ ?

comradesean wrote:

Spent almost $450 on a copy of Ultima II thinking it was for the PC, but upon receiving it turned out to be for the Apple II. I took a further look into the contents and it matches up with every version previously sold (including the errata note saying it's one of the first releases) These generally sell for $150 on eBay so I'm in the process of initiating a return.

However, there's one single difference. This copy included a second write protected (notchless) disk 1. It's still an Apple II flippy disk and while the disk is largely similar in that the Player side is a CRC match and the majority of the Program side is a CRC match, there are a fair amount of sectors on the program side that aren't a direct CRC match to it's counterpart.

Does anyone know what this disk actually is?

It is a duplicate of the Program and Player Master Disk. Because the Player Disk is irretrievably overwritten when you start a new game, you would copy over the data from the notchless disk to the notched disk. The Program sided are copy-protected, the Player sides are not. This is the only way to start a new fresh game, but you can format and copy the files on the Player disk to any floppy disk.

Great Hierophant wrote:

It is a duplicate of the Program and Player Master Disk. Because the Player Disk is irretrievably overwritten when you start a new game, you would copy over the data from the notchless disk to the notched disk. The Program sided are copy-protected, the Player sides are not. This is the only way to start a new fresh game, but you can format and copy the files on the Player disk to any floppy disk.

That makes sense.
Because of the non-matching sectors located in DSK image tracks 10 (sectors 002-009), 11 (sectors 000-001), and 52 (sector 006) and the lack of this disk in other auctions I've seen, would it be safe to assume this is an "after-market" disk requested by the previous owner from Sierra?

The write-protect tabs are still in place and my KryoFlux is reporting all unmodified so these are factory pristine.