We should try to figure this out.
Rich and Roy both seem to have some useful numbers. Let's assume that the width of the MXY (along the length of the strings) has not changed, and that only the hole spacing has changed, but has always been centered.
So we list the latest instrument serial number and date of birth, that has the wide spacing, as well as the earliest with the narrow spacing, and of course say what the wide and narrow spacing is (center-to-center hole spacing, inches or mm, your choice).
Anyone who has conflicting evidence, or can help narrow down the time range, posts that information (maybe we should continue here, since people can't respond to the FAQ section).
It seems like a pretty safe bet that the mold didn't change very often, so maybe we can pin it down pretty closely, and at least let people know what the measurements are.
The Series pickups have been around a lot longer, and perhaps there are more variations, but maybe we could start with Dave's and work backward or something.
And perhaps along the way, we can turn up a set of pickups for Roy.