We designed, implemented and tested enhancements allowing the transmission of richer information from sources, during the metadata transfer, to cater for the case that the desired harvested metadata format evolves. The new functionality will be useful in applications like disconnected health assistive environments that occasionally go online so that their information is polled, especially when the harvested data format is occasionally revised, like when replacing their sensors or their software with different versions. We provide the mechanisms to transfer the raw metadata of each source, while still converting it to the desired format locally at the OAI-PMH client, based on the provided XSLT mapping. The proposed solution ensures full interoperability with non enhanced OAI-PMH clients/servers, so that all OAI-PMH agents can be freely mixed, although the new functionality will only be available to client/data provider pairs that both incorporate the proposed enhanced features..