South American collectibles are very often a real problem. Concentrating on Colombian coloured vinyl 12"ers (Crazy, AOBTD, Pressure) I did some researches, because new vinyl reach the market almost every year and even the "existing colours" vary. The most common colour is (clear yellow) and the second clear green. From Under Pressure I only know of these 2 releases.
The other 2 exist in many other colours (f.e. blue, orange, grey)
I've got 10(+) of these records in my collection and took a detailed look. As an example I describe the yellow AOBTD: I've got 3 different of them, all definitely from different matrixes.
The matrix-numbers are identic in general, but 2 of the versions have added the date of pressing (printed like "27.XI.1980"). Those 2 I bought in the 80s. The 3rd one (bought it 4 years ago) had no additional date printed with the matrix-number.
As a collector you have to define items as "real" or "fake" for yourself. For me I have decided: Colombian 12"ers with additional pressing-dates printed on the vinyl (matrix) are really made in EMI-press factory in the early 80th. All others where done later somewhere...