Have a look...

[eagle_12]

BillyMac

Not a basketball ref, but was involved in basketball operations and dealt with equipment/uniforms in the D(now G)-league 5 years ago.

At that time, what you show is correct in that players could not wear a shirt under their jersey, similar to you see in HS and NCAA. If they had an undershirt it had to be a tank top, and either white or black.

At some point during my 4 seasons, someone (might’ve been Anthony Davis) in the NBA hurt their shoulder and needed to wear a shirt with built in support/compression/protection. NBA said cant do it because it’s a shirt and we don’t allow it. It was later deemed a medical device and then same rules don’t apply.

Now verbiage and allowances may have changed in the past 5 seasons, just sharing what it was during my time.