The border is easy. It is not flat, but flattened. The remains of the teeth are still visible. That could have happened inside or outside the mint. The absence of the dot for Pretoria could have been a dirty die, but I don't see any ghosting.
The round-topped 3 is hard to explain. I have seen only flat-topped threes. The only scenario I can think of is that the 3 was punched in separately to save money at the end of the year. This would have resulted in the final digit of the year being slightly out of alignment in some instances. I am not aware of such coins, so I tend to think that the Indian and Pretoria mints at this time did not use this practice. Also, the 3 on your piece is perfectly aligned.
The crown is impossible to explain. In all three varieties, the lower band of the crown is an oval, so the crown should be described as "like the flat crown". The missing lower line of the oval is highly unlike to have occurred in the design stage, as it is clearly intended to be there on your piece, in view of the two down corners of the band. Moreover, 1943 with this size letters is known exclusively with high crown. This also makes a changed date (1943 from 1945) quite unlikely.
The coin is not a pattern or a restrike. It has clearly circulated. You may argue that it could have escaped into circulation inadvertently, but that doesn't explain the impossible crown. In general, I would be wary of flamboyant varieties of common coins that have gone unnoticed for 75 years.
Peter
