If you look at your motor, you will notice that the magneto armature plate rotates as you advance the throttle. When it rotates, it changes the spark timing related to TDC. So at wide open throttle the spark occurs considerably before top dead center. At slow idle position, it probably occurs after top dead center. How much it varies is fixed by design and is not to be monkeyed with, nor can it even be monkeyed with without re-engineering it.
Now back to those points: The purpose of setting them is NOT to set the timing in relation to TDC, although yes it does affect it a bit. The purpose in setting the points is to make them open at the right time as the flywheel magnets pass the coils' laminated cores. Therefor, any reference you may see concerning timing is about timing the points in relation to the magnets, NOT in relation to TDC.
Don't try to make it complicated. Adjust the points so they open .020" at their widest opening and let it go at that. That's "good enough". If you want to get them perfect, and easier to do, you can use a timing fixture made for the job. But after reading through this long thread, I think "perfect" may be a bit of overkill.
