One of my tasks for Y2K prep was to modify an in-house-developed record-based "database" to accommodate a the century change. Originally developed in the '60s the year had originally been a single digit because everyone thought commercial DBMS' would be viable in few years so there would be a replacement before the decade rolled over. :-| They'd grafted decade handling into the thing before I got there so it could survive the '70s because they had a lot of expensive data in various file sets that contained the data. Converting to a commercial database was expensive and represented a huge business risk, so...