A correspondent has pointed out that an easy way to identify originals of the 1896 issue of El Salvador is to look at the First Issue of 1895.
No reprints of the First Issue of 1895 are known EXCEPT for the unoverprinted ones and those with the coat of arms in the wrong color. In fact, the unoverprinted ones and the ones with the coat of arms in the wrong color exist ONLY as reprints. Thus, collectors can acquire mint copies of the 1895 First Issue with confidence they are originals.
Now, since the First Issue 1895 and First Issue 1896 issues were on the same plate you can use this to determine whether a First Issue 1896 stamps is an original or not. Just, closely compare the paper, gum and shade.
The plates used for these issues were of 200 subjects, 100 of each issue. Here are the known combinations of the plates:
1c + 5c
2c + 3c
3c + 2c
5c + 1c
10c + 30c
12c + 20c
20c + 12c
30c + 10c