All good, I'm no expert myself. I think that both of these part numbers are sorted from the same production process (hence the 'sourced from process 05' on both datasheets) - they're basically the same part. The lower gain ones are marked as MPSA13, the higher gain ones as MPSA14/BC517. Anyway, I'd imagine that for a switching application especially (as I suspect this may be), the precise gain values are of little consequence and the higher gain version could be substituted without a problem.