I don't think the matrix number necessarily refers to A or B side, just a reference to the stamper, as shown by Rod, there is a large gap between one side of Jackey Beavers and the other, and there are plenty of instances where sides are re-issued with different b-sides (retaining the original matrix and not assigned a new one). The plug sides could easily be chosen by radio DJ's and I'd bet more often than not were, regardless of having a plug on them. Just a thought.