I've noticed that some are repeated on the last row.
It tends to run small and some people will size TTS on them rather than going a half size down the way it's usually done for Barrie.
Yeah it can be a little hard to figure out. I tried on a pair of Barrie longwings in size 8.5D and they were definitely too big, yet my PCT boots in size 8.5D fit great.
EDIT: I'm referring to the Alden x J.Crew PCT boots, which by many accounts run small. I'm not sure about other Alden PCT boots.
Here's my experience, fwiw. I went with conventional wisdom and went a half down from Brannock as with all my Barrie boots. They are a good fit although I really can't wear thick socks with them.