Guesses about Tool Storage series

These are my guesses about tool boxes

Snap on purchased tool boxes from an OEM manufacturer until 1958/9.

In 1958/9 they expanded the Algona factory in Iowa and brought the boxes in-house. If you notices the KRA series all start about that time and the KR series holds over, but nothing new is ever introduced with the KR series after 1958.

I think K is originally for Kit
KR is Kenosha Red
KRA is Kenosha Red Algona

I also think none of the boxes are numbered until the KRA series