Quote:
The only recourse is to collect enough stamps to be able to eventually discern a difference?
Sorry, but surely that is the point of stamp collecting - not to have a single copy of something that someone or something has persuaded you is a SG 227Ab(ii) or whatever, but to study the stamps and find out all you can.
If you are really interested in this issue - Get lots of cheap examples. Compare them. Try to get some with clear dates on. Put them under UVF. Read all the literature. Include in that articles on chemical analysis of colour. Make up some pages showing the full range of shade. Try to come up with a sensible analysis of where the divisions are. Find other collectors who are working on the same problem and compare results. Write up your conclusions.
Then come back here and tell us what the answer is

And if you are not really interested in this issue - what does it matter precisely what type it is?