I found a tach board that has a reference corner etched on the board suggesting pad placement might be relative to the corner:
That's an interesting observation about the mirrored pinouts. I suppose the new board could be used for either version with the silk-screen on each side showing version. OTOH, the EE-SY124 is obsolete so why bother...but then again I'd think there are equivalent parts that use the same pinout.
