The couple times I've had to worry about this - if the nut tightens, I was OK. If the nut would just "spin" where it needed to tighten - then obviously it was not going to work, AND I was screwing up my threads - so don't repeat

Some will tell you three full threads is minimum to make it work. To be clear - some of this will depend upon the manufacturing tolerances between your steerer and selected headset.
[If you look at engineering analysis, even full depth isn't enough]

A Tange Levin can be a relatively inexpensive solution in many cases.