The OP's conclusions are askew. If you remove the default contracts from the contracts table you are left with fixed term contracts. This means customers with

The OP's conclusions are askew. If you remove the default contracts from the contracts table you are left with fixed term contracts. This means customers without fixed term contracts are assumed to have default contracts. Agree so far. But removing the default contracts removes the contract start date. Meaning the default start date HAS to be the customer start date and not a separate date. This changes the functionality of the system, not the state representation.