Possible test coin?

I have an item, not in the best of condition but nevertheless interesting.

The 50 cents coin has an obverse of the portrait of Queen Elizabeth II (as per KM# 36) which is couple with a reverse dated 1948 (KM# 30) I suspect that this is a test piece where the newly crowned monarch's engraving was being tested using left over pieces of the original coin. 

I have been unable to find any information to prove or otherwise this and wonder if anyone has any thoughts?

I suspect what we are seeing here is an illusion and it is simply a genuine Queen Elizabeth type with a deformed or altered date. Agreed, the 3rd digit appears to resemble a 4 but it also appears way out of context in size to the 19 and a deformed 4 at best. The 8 less so but still does not look quite right relative to the size of the 19. I believe the last 2 digits were added after the fact during the year they happened to be minted as well. To state or assume that this is in fact a 1948 date is a stretch from the start. History has not been kind to this example and it could be explained away as environmental damage which deformed the digits giving the illusion of a 1948.