Yes my very limited experence with the keys is the first digit is the key blank type and where the slots in the key blank are located and the last three digits is in regard to the tumbler cuts in the blank, i have noticed that some keys with the same last three digit numbers will work or may work check it out Regards Tom
I sold my first Sandcast and regretted it till I bought it back 6958/7149, its taken a few years to get a couple more 6946/7169, and 6970/E6956