Just from personal experience, the chance of the lock still having the same tumblers that matched the code after all these years is slim. Most of those locks had a clip on cover that allowed access to the tumblers. The tumblers were each a two part combination with a longer to shorter "follower" with a countering part that springs pushed on. Each combination totaled the same length. When the key was inserted, the parting line between all tumbler pairs lined up. The code on the lock originally could be looked up in a master book that told which pair went in each particular slot. Anyway, a good locksmith should easily be able to make all of your locks work with the same key.
