Let's see if I garble this one up- you guys know how I get details out of whack going from memory(it's that darned CRS).
The story I was told is that at one point there was a rather hasty change in manufacturers. To prevent a lag in having the products available, the first run of machines by the new manufacturer were from heads(or parts thereof) that had already been built. Then after that first run the manufacturer started using Sears' proprietary specifications.
Cari