Emu (Early Matching Usage)... What's The Date Cutoff?

I've never seen this clearly defined anywhere, and presumably it's open to interpretation. I've always considered the end point to be March-April 1863. However, I was just reading through a Mike Mahler exhibit where he calls a September 1863 usage an EMU.

That sort of shocked me, but Mike's forgotten more about revenue documents and rates than I'll ever know. That just seems extremely late to me to be considered an EMU.

Thoughts?

Oh, so that is what an EMU is! I thought an EMU is a soft-feathered, brown, flightless bird with a long neck and legs that can reach up to 1.9 meters (6.2 ft) in height.

Seriously, though, Mahler states in his book that the rather soft cutoff date for EMUs is June 30, 1863. The key word here is "soft;"

So when you're selling it's an EMU, and when you're buying it's not.

"This document is EMU-ish!"

I think it depends a lot on specifically what the stamp and the usage is.