Many of us have long since concluded that the clearly superior proofs of the late pre-decimal era were not labelled as "VIP" or even "Record" & this seems to be either/or invented terms of convenience and marketing (both?) but that it really doesn't matter as they "are what they are". In other words, and particularly of non-standard years, specimens of coins exist that are not run of the mill or willy-nilly early strikes, or whatever; most definitely are exceptional pieces that appear to have been produced with special proof qualities such as are generally are known.
Bull is in all likelihood INCORRECT in separating, especially in the off years (and to some degree those from 1911, 1927, 1937, 1950, 1951, 1953 but also the 1960 crown) into ordinary proof and VIP/record proofs. In fact I know some of the principles you have referred to and can tell you that they agree. I do not know Mr. Bull but I would imagine that the difference he refers to may be that some have a cameo contrast between fields and devices and others do not. What we choose to label them is artifactual, but these superior piece do exist and that is clear.
As a bonus point: regarding crowns of especially 1937, 1951 and 1953 years there appears to be some confusion - and I will admit to not being clear myself. I believe it well nigh impossible to differentiate between those with exceptional strike and cameo contrast between fields and devices, and those labelled as "VIP", "Record" or any combination of such. There are some exceptions such as the 1953 penny where even amongst the better quality proof strikings that there are die differences with the rarer types different enough that they fetch much higher prices on the market.
I will confess to having purchased a 1937 proof crown as "VIP" (or similar designation as I can not remember) from Baldwin and paid significantly more therefore. When I later compared it to a slabbed and graded Proof Cameo 66, I could detect no meaningful difference with the latter generally somewhat superior mainly in that there were less handling marks, etc. I have learned my lesson.
Further, a somewhat similar situation to the purported silver strike 1960 crown are the types of 1935 proof crown: specimen 0.500 fine PL coins, proof raised edge lettering coins, proof 0.500 and proof 0.925 incuse edge coins.