Yes, I did indeed make a threading error, leaving out a repeat of a block.
Once seen, cannot be unseen. But, on the other hand, the 'flaw' won't in anyway affect the ability of the tea towel to dry dishes, so I'm not fixing it.
I am, on the other, other hand, dealing with another loom issue. While the dobby head seems to be fixed, one of the shafts was not perfectly straight and because it was dipping downwards on one end, the warp ends on that shaft were not lifting as much as they should be doing and I realized well into towel number three (the first one after the dobby fix) that I was getting really (really!) long floats on the back side. Which, in this case, is going to be the 'correct' side of the cloth.
After complaining about the issue, Doug has effected a temporary 'fix'. I'm too tired to weave now, plus it's time to make dinner, so it will wait until tomorrow to see if it is going to allow me to weave without stopping every fourth pick to make sure I have a clear shed.
The first three towels will go into the 'seconds' pile.
Still not perfect...