Part of the difference could be number of manuals versus number of different manuals. The original blog post talked about there being multiple cookies of some manuals.

Part of it could also be ronding up for advertising a number they do not know exactly. A firm like this may not have kept perfect tally of their stock ("hey guys! It's January again. The guy from accounting needs to know what we have. It's counting time!")

A big part of it was that they were definitely further up a year or two ago and have been trying to fire sale out manuals as they go. The website has been updated infrequently so the number is not as large anymore.