OK MOTHERFUCKERS CHAIN BREEDING QUESTION

Its possible to get evee to learn wish, even though it never learns it through leveling, nor is it possible for a valid farther to give the move via breeding (ie there are not farther that can learn wish in evee's egg group)

The solution is for a second pokemon (say togetic) to give the move to something that CAN learn the move and IS in evees egg group, then breed THAT with an evee to get the move "wish" passed onto the offspring.

My question is this, how the fuck did someone work out that evee can learn wish? Are there any rules as to what egg moves can be learned using this method?

FOR EXAMPLE: Poliwrath cannot learn skullbash, yet using the logic above a marrowwhack knowing the move could pass the move onto a male squirtle child, which could in turn pass this onto the poliwag child.
BUT THIS DOESNT WORK.

Is it just pure trail and error? Are there people in japan endlessly breeding pokemon over and over in every possible comination to see what works? Or is there some logic to the move distribution?

Pic unrelated