FWIW Dept.

I have come across a couple of Bulletins that lead me to believe Teletype changed their revision scheme around late 1955.

For example 1124B of October 1955 has the pages and "change in effect" all marked as ORIGINAL, but it also says "Supersedes May 1949 Issue 5"

Thereafter, revisions are referred to as Change 1, Change 2, etc.

1037B of January 1956 is a little more confusing - the cover says it is Issue 6, but the pages and "change in effect" all say ORIGINAL