Ed and Margaret Burke's work is marked EM. (I've got a lovely bowl).
Sometimes, owners of bits of glass write things on them, such as their own names. I'm not saying this has happened here, just that folk should be aware that it can happen.
What is written on a bit of glass can sometimes confuse, more than assist, identification.
Adam Aaronson has told me that this partial casing by side-dipping is a technique most glassmakers learn nowadays.
In answer to your question though, I think it is definitely NOT tat.