I'll only say that 95% (at least) of U.S. studio glass is/was signed & that goes back when the wave first hit. You might not be able to read the signature or they might have been in business for a short period of time, but they signed it...after all most of these people were trying to build a clientele & make money. There were hundreds of these studio operations in the mid 80's, but a decade later 95% of them were long gone & the movement was dead except for a few that managed to succeed. Ditto to Art pottery during this same time period.