The following list may be helpful. It is a rough picture of the serial number ranges I have observed for the first few styles of badges:
1 - 749000 Keystone
749000 - 2120000 Blue/Olive with Pointy Corners
2120000 - 3131000 Blue/Olive with Rounded Corners
Note: There were several odd badges along the way.
1. Keystone Badges without serial numbers that appear in the September 1970 time frame.
2. Pointy corner B/O badges without serial numbers that appear in the September-October 1970 time frame.
3. Pointy corner B/O badges with hand trimmed corners in higher end of serial number range and transition to rounded corner B/O badge.
4. Pointy corner B/O badges with the bottoms trimmed off to fit the higher vent hole location on some snares (presumably drilled for Keystone badges).
5. Other oddities that may have been factory or may have been post-factory modifications/attempted restorations.
Rick