Gibson F5 Fern joint

[Benjamin T]

Do we know exactly when the compound dovetail joint entered into production on the F5 Ferns produced under Mr. Derrington?
From what I can tell through research, is sometime in 1999. Do we know the month or date?
Can one tell if an instrument has and M and T joint versus the compound dovetail by serial number, luthiers mirror, magnet, etc?

[Big Joe]

The only way is to look inside the instrument. You can remove the end pin, then shine a light in the F hole and you should be able to see the headblock. If there is a bolt in there, it is M&T. If not, likely a dovetail.