David — thanks for considering this and giving us your opinion. I can't help but agree with you, but it still leaves me worried.
The earliest Masey I found was in BGbtW, 1987. All of the other Masey spellings are in that Broadfield House group of references, and could originate from BGbtW or from Dodsworth's original source. Ellis lists BGbtW in his bibliography, so he must have seen the Masey spelling. His book is about the people who made the glass, and so the names must have been checked over and over again as one of the most important aspects of the work. Why did he change the spelling?