I'm a bit confused as to what you mean. Arabic is an alphabet. It's a cursive alphabet so the letters are written differently based on their position in the word (i.e. Initial, medial, final or unnatched.) The script has gone through a number of variations over the centuries. Early Arabic script doesn't reliably use dots, for instance. The introduction of other languages that used the script necessitated new letters. For instance the Persian "V" ڤ. Or the Urdu "g" گ.

There are also a great number of shorthand or alternate script ways t write the same letters.

All of that being said I'm not entirely sure I understand your original question. Do you mean like a ي with three dots or something? Not that I've come across. Where other combinations are used its to necessitate the needs of other sounds in other languages. As far as I'm aware, Hebrew has an almost identical set of sounds. It's simply a feature of Semitic languages, not that there were other sounds that were somehow made "obsolete."