" if you find yourself with a full buffer that would be an error condition. You'd normally send some kind of NAK message to have the sender re-send the data.
"
That wont work in in receive only mode like reading data of a gps receiver.

It looks like there is very little difference between linear buffer and circular buffer. With linear buffer you reset the buffer once you processed the message while with circular buffer you dont need to reset anything.
with linear buffer if you get overflow do you reset the buffer(receive only mode) or what ?
if answer is yes then you lost sync of your message and might never be able to recover your framing error. What you have to do is work on byte level and shift left till you get your framing correct.