THC-A is the acid form of Delta 9 THC. Marijuana has mostly THC-A that doesn’t turn into d9 thc until it is decarboxylated. Look at any test result COAs of marijuana to see what I am talking about.
THC-A hemp is just marijuana that isn’t considered marijuana until it is burnt. Hemp is just cannabis. It is all cannabis. The same cultivars are being used for THC-A hemp as medicinal and recreational. In fact, there is genetic bottlenecking going on.
As you said though, cutting early generally ensures that any cultivar doesn’t “test hot” for d9 THC. Besides sufficient heat, THC-A turns into d9THC through oxidation as well as UV exposure so the sun isn’t necessary. There is plenty of THC-A hemp flower being grown indoors too.
Happy to answer any further questions.