Yes. Manumarks help date a match. There are lists of all the manumarks used by each manufacturer so it's not a question of having to find an infinite number of varieties for a particular match. However, for big clubs that have been around a long time and placed many reorders, there can be 20-30 different manumarks for a basic cover design. Caesars Palace and Stardust come to mind.

And don't forget to look INSIDE the cover. Many varieties are produced by small (or sometimes major) changes to the artwork for the inside of the cover.

And finally, remember to look for telephone number variations. The old light green/white Tropicana front-striker with the folies berge`re dancer has at least five variarions on the phone number!