That method generate a suffix for a combination of author/year/pubmedID.
The syntax of the suffix is:
[optional char]-[integer going from 1 to n]
if the same combination of author/year/pubmedID is given many
times, the integer is incremented.
if the combination author/year is given with different pubmedID, then we
add a character
example:
jonhdoe / 2005 / 12345678 ----> -1
jonhdoe / 2005 / 12345678 ----> -2
jonhdoe / 2005 / 12345678 ----> -3
jonhdoe / 2005 / 12345678 ----> -4
jonhdoe / 2005 / 87654321 ----> a-1
jonhdoe / 2005 / 87654321 ----> a-2
jonhdoe / 2005 / 87654321 ----> a-3
jonhdoe / 2005 / 11111111 ----> c-1
jonhdoe / 2005 / 11111111 ----> c-2
jonhdoe / 1999 / 99999999 ----> -1
jonhdoe / 1999 / 99999999 ----> -2