Steve may be able to decipher better than I (or have a better answer!).
I'm pretty sure I can. I seem to remember puzzling this out years and years ago, so let me see if I can work my way through it again.
A new taping week started with 9104D. Barker's Beauties Month started with 9111D, and they planned to skip over it, so they did 9104D and 9105D and then jumped ahead all the way to 9151D through 9154D. Evidently, they'd planned to tape 9155D through 9165D at the following session, but for reasons that I'm assuming are related to the Northridge Earthquake, that got cancelled, and those shows ended up not taping until after all the other ones we're discussing.
Anyway, when they did get back in the studio, they started Barker's Beauties Month. Each session, they'd tape the five shows for one of the four weeks, and the sixth taping would be an episode for week 917xD (Monday through Thursday). At least some of the sixth tapings had staffers acting as Barker's Beauties -- I'm not sure what they did on Monday and Tuesday, but they had Sharon Freim on Wednesday and Fingers on Thursday.
After all that was done, they jumped back to the cancelled tapings. The session after that, they started with 9175D and 9182D and went forward from there.
Finally, there is no 9181D. As far as I can tell, it was scrapped to make room for 9041D, which I assume was pre-empted by coverage of the earthquake.
Oh, and for all that confusion, they ended up not hiring any of those models, anyway.