After a few more miles on the treadmill, I reached what I believe to be a little past where the armholes should begin on my Garter Stitch Jacket.
Normally, I count the rows between the front(s) and back to make sure that the body is the same length to the armholes. But, because the fronts were worked sideways (with vertical instead of horizontal garter ridges), the row-counting trick won’t work. Instead, I put the back on a spare needle and blocked it as I blocked the fronts. Then I placed the pieces side by side to check the lengths to the armholes.
The back was about 4 rows too long.
After ripping out the excess rows, I’m ready to begin the armhole shaping on the back. I’ll discard the kinky rip-out yarn, which could wreck havoc with my gauge, and continue with fresh yarn.