Question about sideplate numbering convention

[Edward Tinker]

Here are three DWM sideplates. One is a 67 - it is a orphan sideplate

The other two come from guns that are both police, but appear to be original sideplates.

1st one is the 67 - front is last two of 78

2nd one interior # is 7 - which came off my matching 724 -exterior is 24

3rd one interior # is 32 - which comes off an original sn of 3242 - exterior is 42
(which comes off of an interesting one, one of those with the #8 in the front of the original 4 digits. So its sn now is 83242)