John,
Unfortunately if you want an Iso standard you need to pay for it unless you are a member of the orginization. Even the public library has to pay for them.That's how those orginizations support themselves. I no longer have access to them. A set of all of the standard books will fill a library.
Most of the info in the Threading on The lathe write up is for imperial threads but you may want to do a quick read of it. If you have a machinist handbook you can find what you are after.
The reason it is all so confusing is that everything is based on tolerance that is related to some class of thread and profile and how it's will be applied to what you are going to do with the threaded piece ( ie. maybe you are going to plate the thread ).
One of the things that screws up a thread is not accounting for the cutter tip radius. I usualy do a light finish cut with the threading tool, measure the turned diameter, then back the tool off the piece by the tip radius ( which i know or have measured ), set the major diameter to it max allowable , and base the depth of cut on .866P. Tip radius, even a sharply ground V is not truely "zero".
If all was perfect, the lathe system, the cutting action, setting of the tool, stock support, etc.....you should be able to be in spec.
But in reality "perfect" never happens, so recomend you try experiment some for experience.
RICH