[arethuza]

I've seen similar problems with systems that have supported multiple versions of the same XML schema at the same time - rather than taking the hit of migrating existing data to new schemas you end up having every more complex application code that has to check where a particular value may be stored (because nobody, in my experience, every bothers to store what version of a schema a particular document used).

This is particularly bad if these changes are small and incremental as each one in isolation looks reasonable but the cumulative effect over a few years can be a complete nightmare.