My bad, downstroke of 'd' not '3', now corrected.
I look at transient flaws, the result of a passing problem (e.g. something adhering to the printing plate or an inking problem) as less valuable than constant flaws where damage to the printing plate creates a longer-lasting flaw that requires some mechanical internvention (e.g. retouch, re-entry, cliche substitution) to correct.
Of course, transient problems can serve to create some great varieties (2½d Kangaroo below sold for $53,500 in 2013 but is just a transient inking flaw).
'Flaw' and 'variety' are interchangeable descriptions to me.
Stamps such as the postage due, with the frame printed in a separate process to the value are interesting as sometimes (often with Australian postage dues) the value plate placement was not constant in relation to the frame plate.