Regardless, the basic issue is multiplexing the data. It would seem to make sense not to recitify the data too soon. You also need some way to contend with multiple writers, especially when the write changes the GPS in some way, but even when querying for certain information and providing that data back to the correct client, and not to others.
If you're passing a query through to the gps receiver, the response can be received by all receivers safely. Those which don't want to use that data can just ignore it. If it's a sentence they parse, they use it, otherwise they don't. No harm, no foul.