Chris Pantano employed several glassblowers to make his designs, including some like Jonathon Westacott who were highly skilled and experienced, without them being attributed in the signature. We can speculate what is different here, but it is more likely that MG was a visitor rather than an employee and that it was a collaborative work. Mark Galton had a close relationship with Chris Pantano, having helped to set up Pantano's studio in 1987 and train the initial staff. The initials MG on the OP's piece correspond closely to Mark Galton's handwriting.
Trevor