Custom Schemas for CareFlow EPR (System C)

We've just started using Health Connect and I've found that a lot of the messages we get from our patient admin system (System C's CareFlow EPR) don't match the standard 2.3.1 schema (eg 2.3.1 ADT A02 message spec doesn't include NK1 segments, but the ones we receive do)

Does anyone have a custom schema they use for messages from CareFlow EPR that they'd be willing to share?