Thanks for all of the replies.
Sanford: I didn’t apply the pressure to the base of the tooth. I did them all the same and most bent okay but some (4) just snapped right off.
Can steel get brittle? Well I don’t know the technical term but if you bend a piece of metal back and forth repeatedly it will eventually fail and crack along a straight line where it’s been bent.
Larry Geib: Thanks for a very detailed answer – rust is maybe the issue since the old Groves saw had been lying in a shed for probably 50 years since it was last used and I did clean a lot of surface rust off (with sandpaper, by hand).
Austin Connor: I didn’t reverse the tooth direction because there was zero set left in the saw when I started, however I’ve no idea how the teeth were aligned 100 years ago.
I used the saw yesterday and it cuts okay so I think I’ll just live with the defects for now.
Thanks to you all for helping.