(sorry for English) I agree that we need a better way to represent temporary identification numbers, and that way should extend on the proposed approach of using different system identifiers. The issue with using different system identifiers alone is that unless you embed the semantic meaning that this is a temporary identifier into the system, you don't know if it's a temporary identifier or not. And actually you should not do that, since FHIR's identifier datatype has a type element with an extensible binding to the IdentifierType valueset, which is a good fit for this information. My proposal is that ILCore extends the IdentifierType valueset to add a code representing a temporary ID. This way, we can have identifier.type = "temporary", identifier.system = "whatever it needs to be" and identifier.value = "particular patient". Thoughts?