In my neck of the woods, we see a lot of 19.2 OC in homes from that era. But, depending on your region/state, there may have also just been no enforced building codes at the time… meaning it very well could be totally random.

I’ve seen “headers” over main entry doors made out of weird shaped scraps of beadboard of all stupid nonsense.

A lot of times they just used whatever bullshit they had within reach. Especially in depression era buildings.