ahhhhhhhhh, I didn't realize that. Thanks for pointing that out. So does the two fret difference get us close enough to 24", or exactly 24"?
It is not the number of frets difference, what is important is that there is a 24" scale created between the nut and bridge so that the fret placement for a 24" scale neck will work when putting a Mustang neck on a 7/8 body.
You need to look at it this way.
There are two scales, a 24 3/4" and a 24" scale, being discussed, each of which has its own mathematical spacing for fret positions along the length of that scale between the nut and the bridge. Those mathematical placements for frets are different for each scale, with the smaller scale having less distance between each fret than a longer scale.
A Warmoth 7/8 neck and body go together and there are 24 frets on that neck
A Warmoth 22 fret Mustang/Jaguar neck due to neck pocket placement etc will work on a 7/8 body as the nut and bridge positions create a 24" scale suitable for the fret placement of that neck to work correctly.
Where the neck and body join is also important. See in the next sentence regarding neck pocket placement.
Over the years people have asked can I put a 22 fret strat neck for either a 24 3/4" conversion neck or a 25.5" scale on a 7/8 body, the answer to that is no because in these cases these things will not intonate as you end up with a different scale between the nut and bridge to create the scale length required for the fret positioning on those necks.
But slightly off the question, but still relevant.
What if you took a vintage spec Strat neck blank with no frets on it yet?
There is enough room for a 25.5" scale for 21 frets or in the case of a 22 fret neck which has an overhang 22 frets.
What if I made a body and positioned the bridge for the same type of neck for a 24 3/4" scale by moving the bridge closer to the neck pocket?
My neck blank does not have frets yet so I put in 23 frets spaced for a 24 3/4" scale and voila I have a 23 fret guitar.
This is basically what Warmoth did to create the 7/8 and is explained in the below video by the intrepid reporter
@aarontunes