Has anyone researched the issue of the legality of using prior
Interbase client licenses against Firebird?

I'm in a situation where I have an app in Interbase 5.6 and I'd like
to replace the server with Firebird 1.5. The client apps (Delphi
apps) are installed with a the Interbase 5.6 client, and all tests
seem to indicate that this setup works fine after backing up all
database files in 5.6 and restoring to Firebird 1.5. I want to keep
the 5.6 client because I have a reserved word compatibility issue (a
field named "TYPE") using the Firebird client and the built-in
versioning parser in Firebird makes this a non-issue.

The Interbase 5.6 license text doesn't address this issue well... it
talks about the requirement for the proper number of concurrent
licenses for the server (which we have for the 5.6 server), but with
Firbird this isn't an issue for obvious reasons.

The Interbase 5.6 client also works well as a Firebird database manager.

Any thoughts?