Not sure about your more general question on 241 vouchers. Re-separate bookings, however, you can through check luggage on two separate BA itineraries without needing to link PNRs, and conversely, linking PNRs does not protect you at all in terms of missed connections so you would need to plan plenty of time between your arrival from itinerary 1 and departure from itinerary 2 (and vice versa on the return). In a nutshell, linking PNRs has extremely little interest, except to 'inform' airlines (of continuing itinerary or in other cases of two people travelling together) but without much practical effect.