| Yes, under some circumstances, adding spacers (washers) will add additional clockwise adjustment to a truss rod nut that has "run out of thread". However... it is not a cure-all. Here's my story...
My main player is an older MIA Fender 62 RI Jazz. By all standards frequently discussed here, the truss rod nut had "run out of thread" and would benefit from the spacer remedy. I tried it. It didn't work for my instrument. The truss rod nut would only tighten so far and then refuse to go any further. And I still wanted less relief.
Next I took off the neck (no big deal if done gently and properly), removed the truss rod nut and counted the number of turns it took to remove the nut. After the nut was removed via 8 turns, I took a bolt and threaded it into the truss rod nut... 19 turns!! So that proved to me there was plenty of thread in the nut. And my previously trying the spacer technique didn't work either so that proved to me there was plenty of thread left on the truss rod itself.
My final step to resolving this involved supporting the neck on 2 pieces of foam... one under the nut area, and the other under the heel end. Gently pressing down and then releasing pressure (I call it wiggling) on the center of the neck, while at the same time trying to tighten the truss rod nut...... I was amazed at how easy it was to tighten the truss rod nut while "wiggling" the neck.
What had apparently happened was that the truss rod was rubbing and/or tightening against its slot in the neck (maybe the slot was cut a bit too small?) and the additional friction made it feel like it was running out of thread. But in fact there was plenty of thread left on both the truss rod and truss rod nut.
OK, I know this is a long response... but I think that "just add spacers" is a frequently mentioned cure-all to truss rod issues... and I just wanted to share my own experience with how I diagnosed and resolved a problem I had with my instrument.
And for all those who think I went through too much... that jazz bass is now the only instrument I play, and I own a lot of bass guitars. It's the first instrument that just fits perfectly, and I've played plenty of jazz basses... some intangible mixture of weight/balance/voodoo... can't explain it but my efforts were completely worth it.
Hope this post helps someone.... | 
