Nice find - you often see odd ones, but complete sets are not so common. I haven't yet determined the dates of the different glass types: clear, enamel-sprayed, opal-flashed* and opal, but I think opal and clear started quite early (pre-1960 onwards) and sprayed-enamel after 1970.
*Opal-flashed I have to determine, but it is possible they were made c.1960 onwards