The NAUI standard requires that technical (Intro, Deco, ...) training classes follow NAUI Technical Equipment Configuration. The most recent copy I have is 2010. It says, with emphasis mine:
"
Twin primary cylinders connected by a
dual-port manifold with an isolation valve are required for
all training that will involve actual or simulated decompression stops. For training that does not involve decompression, a single primary cylinder with an “H” or a “Y” valve is acceptable."
...
"
A wing-style buoyancy compensator is required and may be mounted to either a hard backplate harness or a soft harness."
https://www.epicscubaadventures.com/wordpress/wp-content/uploads/2016/03/NAUITechEquipmentConfig.pdf
Are you suggesting that they geared up on the boat in singles, inverted ponies and jackets, and then the instructor said 'no, no, no, you need doubles, lets get you changed out"??