There is a bug, I have Dondozo but can't get Tatsugiri and the game won't let me buy any more eggs. I know from a different save Tatsugiri should just be a normal egg Pokemon. I have 115/142 Pokemon with no challenges done with only Luvdisc, Chatot & MissingNo being my non-egg Pokemons. so my number should be 112/142 if you ignore those. Also I have the Pokemon listed alphabetically, I promise you it isn't a case of me just being blind.
Correction: Shedinja is also technically a non-egg Pokemon, did you remember to factor him in? If counting Shedinja as a non-egg then my number should be 111 (110 if counting the starter as a non-egg) eggs. I feel if a bug going to exist it will be due to the number being weird.