Many thanks to each of you for your thoughts on this thread. Maybe cameron2trade has it right, by the time someone comes looking for firearms, it's probably past time to be gone anyway!

Sounds like it comes down to:

Private transaction: good idea to have a bill of sale/receipt to provide some measure of arse-coverage in case a firearm has a bad history

Public (retail/FFL) transaction: paperwork/background checks are completed by retailers; datamining does not require much time or effort should someone what to run searches on ownership/registration details.

Guess it's like many topics these days: one's expectations of likely/unlikely scenarios directs one's risk management decisions.