I've successfully homed a 406MHz beacon without any info from the satellites. It wasn't easy, but we worked it out. If there are two continually transmitting beacons close together, I can home to the stronger signal, but with 406 beacons if two are transmitting near each other it will be nearly impossible for me to resolve either one. This may change with homing technology, but even better is to ensure that the GPS is a part of the 406 and that the beacon also transmits low power on 121.5. Having the GPS external only helps if you're a cooperative crash victim, ie when you don't need rescuing as quickly. GPS technology may be changing rapidly, but most rescuers will find you if you get them within one mile...meter accuracy is not required.
Matthew.