Extension on a petite bouche

juanderer

Any reason why they don’t have extensions when some D-holes can go out to 25-26 frets for the high E & B strings.

That's precisely why. It's common selmac nerd knowledge that those fretboards were originally intended for the D-hole design. The instrument Bireli is playing is a throwback tribute to those few specimens of Selmers that were made during the transition from the D-hole design to the oval hole one when they did away with the resonators and were using existing parts stock because it made economic sense - especially considering the supply chain challenges of wartime. EVH had frankenstrats, Django had frankenselmers.