Numbering of double length episode


I have a question about numbering. I have a M.A.S.H. recorded from Czech TV station and have some problem with few episodes.
For Example in Season 4, there are 24 episodes according to opentvdb, however according to Wikipedia (and also our TV station), it has 25 episodes. It is due to the first episode is divided into 2. How should I name the files? Now I have:

Mash S04E01a
Mash S04E01b
Mash S04E02
Mash S04E03