I was taught to check if a timing chain had jumped a tooth (particularly cheb plastic gears), that to put #1 or #6 (or#1or #4 on 4 cyl. cyl) in overlap.
If the timing mark was more than 12*, the chain had jumped, not stretched.
Proved true time and again.
That was my test
the chain has to have stretched a lot to jump teeth, if it's not stretched ie correct tension it can't jump. now installed a tooth out? that's entirely possible, lol.