It appears that you're correct. The 100 came first, then the 100A (100AP), then the 100B (100BP) - it appears that the P signifies the North American version.
At first glance, it does appear that there's a bit of inconsistency here, yes. There are some improvements from the 100 to the 100A.
You've probably done this already, but for further reading, take a look at this and similar pages to determine whether you'd like to initiate some kind of return/exchange/refund action - good luck dealing with whoever sold it to you:
http://www.adamwilt.com/24p/index.html