Did it come with USB to Ethernet adaptor? I am not 100% sure date would verify it, because when they refurbish them they get a new date. There is no technically different model number, and Apple did sell 1.86 GHz rev B's with 120 GB HDD. It would have just been a CPU bump for $300, isn't that what they charged for the rev "B" MBAs? So it would have been $2099 if it were a rev B custom configuration model. Otherwise it would be a rev C for $1499 new - BIG difference there.
All the rev A, B buyers really got a terrible deal from Apple. Not only did Apple drop the price to dump the MBAs, it didn't help anyone out on the problems of the original MBA nor the ridiculous price drop from one day to the next with the so called rev "C" update.
The full charge capacity of the battery should be higher on a rev "C." It should have an Ethernet adaptor standard. Only rev C's would ship with Snow Leopard, but some rev Cs bought in June/July 2009, got upgrade disks to Snow Leopard so could have shipped with Leopard. One last thing that probably nearly guarantees it's a rev B and not a C is if the display model number is different from all of the Cs reported with the exact same display. There were some Bs with the display, but most of the Bs had two other display model numbers.
Anyone else think of other ways to identify the B from C? When it's a 1.86 GHz and has 120 GB HDD?