Interesting how time flies Wade... I have been rather busy this year. Anyway your logic would be correct; the "B" may only be significant with respect to the builders mind set at the time. If we had been sitting around and brainstorming idea builds this one might have been my idea ie "exp-B" . yours would then have been "exp-W" and so on for every test example we would be comparing. the fact the "EXP" is followed by another character lends to the thought there were more than a single piece made. We could speculate over the logic surrounding the numbering and never really know for sure why,unless we were informed of the rational by the assigner of the designation.