The problem was that the names are too close to each other and was one typo away from mysterious bugs. The non-existence of documentation didn't help either.
If you go that way there is also MD2_Update, MD4_Update and MD5_Update, that are also one typo away of a bug you can't miss at all if you test anything.
Of the many many faults of the OpenSSL API you just didn't chose the right one.
