A coin question.

I am posting this picture for a friend of mine as he knows little about this and I know even less
The coin in question is the one on the right.
I'm using the other coin to show an example of the difference between a normal silver coin and post silver production example. You might note that aside from the last digit of the date which shows a hint of being a 7 (seven) it also has several other obvious differences, which in my opinion erase any thoughts of it having been altered.

Remember since silver production occurred only between the years1946 and 1964. and it is obvious the third digit here is a 4 thus the coin would have had to have been produced in either 1946-47 48 or 49
The fourth digit shows signs of it having been or intended to have been A 7.but I'm not sure.

I'm trying to find out if this is unique or if there are other examples of this around. a
At the same time if anyone has any idea of what the value might be any help on the subject would be appreciated

In any case any information anyone might have in regards to value how this happened or anything else would be appreciated .