There are two types of signature.
mostly items say simply 'Max Verboeket - Maastricht'
Sometimes there is a number which represents a unique number for each piece usually a model number (three digits) followed by a dash, and a sequence number.
There are some records from the factory which give clues as to dates and numbers of items that were made, but research suggests that the lists are not complete or correct. (Ask me)
There ARE unmarked items in circulation and not many people that doubt they are correct, made in the factory, etc. During this period the factory was being 'wound down' and the glassblowers were NOT happy. It might just be coincidence (or not ?) that the quality of their work, sticking to the design parameters, and signing pieces properly, all seem to have become irregular habits (imagineded to be caused by lack of interest, and disillusion with the factory owners.)
Collectors still prefer signed items, but colourway is more important. Unsigned items are probably later than signed ones, but it doesn't really impact on the market/price.
FYI this is quite an unusual colour and therefore a bit more desirable than average.