ASME
The Van's KAI Section 5 has a very good description of torquing and discusses friction drag, which is technically "prevailing torque". I recommend reading that section rather than restate it all here.
Prevailing torque is almost always within 5% of the total torque, but more on smaller fasteners, less on larger ones (depends on the fastener retention mechanism, i.e. elongate thread, nylon locking, lock washer, etc...) and whether dry or lubricated threads, or if it's a previously used fastener.
I wouldn't stress over it, just measure it.
In reality, most fasteners have +/- 5% torque tolerance available - some much more. It lines up well with the 3-5% torque tolerance of torque wrenches. It's almost like a bunch of engineers got together and planned it that way
More food for thought - how many people actually get their torque wrenches calibrated every 12 months (or a certain number of cycles if more often)? It's actually the ASME standard and required for most certified work. But I'd guess not many folks do, especially for personally owned torque wrenches. I'm pleasantly surprised when folks even
USE a torque wrench. I've observed many people, certified mechanics at that, use the "that's about right" torque setting with their "calibrated" hands.
So, the fact that you know the required torque setting, are actually using a torque wrench (properly I hope) and measure the prevailing torque first, then add it to the final torque - well, you're ahead of a lot of folks. Now, if you're doing so with a wrench with a known, valid, calibration, you get bonus points.