Watched my neighbor do almost the exact same thing last spring. She had her starts in this dark corner of her shed on a beat up folding table, and they were just sitting there looking sad and leggy. She cleared out a bunch of old paint cans and junk, put in two cheap wire shelves by the one window that gets sun, and switched to those little fabric pots so the roots could breathe. Two weeks later her tomatoes were twice the size of mine and I was honestly a little annoyed about it. She didn't buy a single new light or fan, just moved stuff around and gave the roots somewhere to go. Makes you wonder how much of this hobby is really about gear and how much is just about light and airflow.

My buddy hit the same thing last fall when he was finishing his basement. He was nailing up furring strips and one stud just blew apart right down the middle, about a foot of split. He cussed for ten minutes straight and his wife came down to check on him. He ended up doing the same thing you did, sistered a new board on and patched the drywall after. The kicker was he found two more studs with knots in that same wall so he went slow the rest of the day. Sounds like your house is from the same era as his, so dry old lumber with hidden knots is just par for the course. Six hours a day two days in a row is rough but at least you caught it before the closet went in.