I've seen several Hoboken-era Guilds in which the finish on the headstock is matted (I owned a '68 F212-XL with this).
I'm not sure if the factory did this or someone else after the fact, but I suspect it had to do with some performers wishing to avoid the reflection of stage lighting. This would have been particularly notable during TV performances.
Patrick Sky's Guild here (an F50-R?) I assume was made with these modifications at the factory ... because this particular guitar is not only matted on the headstock and entire finish, but also is missing all inlays on the fretboard (another element that could cause unwanted reflections):
*Patrick Sky had some kind of endorsement deal with Guild, based on this ad:
Interesting that "Sound Rocket" mike appears to be an AKG D202 ... I used one to record about half of my recent record, great mike and very peculiar design.