Question about rear wheel eccentric pinch bolts

[Pasop750]

I just removed the rear wheel to get a new tire fitted. The lower pinch bolt on the left side eccentric was really hard to undo. I got it out after heating things up a bit but the threads on the bolt look damaged. I used one of the other bolts to check that the threads in the swingarm were OK and I noticed that the bolt would only screw in about 2/3rds to 3/4 of its length before it hit a dead stop. Checked the right side lower and found the same. So I'm guessing the two lower holes in the swingarm are only threaded part way, so have to be careful not to over-tighten the two lower bolts (which I think is what damaged the threads on the left side bolt). Has anyone else come across this?