But is that 2 million+ the whole mintage or just the mintage for die #34? I have no idea if that is a rare die number, but i also suspect there aren't a lot of people collecting half sovereigns by die number. Could be a case of the collectors being rarer than the dies.
While it doesn't answer your question and you may already have this info, here is a list of known die numbers in case others are interested www.coins-of-the-uk.co.uk/dieno.html I also found a listing for the following book. No idea if it lists die number rarity. There may be a 3rd edition in the works 2004 The Gold Half Sovereign by Michael A. Marsh, published by Cambridge Coins, Second Edition, ISBN 9780950692951