51 Modifier Question

I'm not sure if I'm using this modifier correctly.

My understanding is that if multiple bilateral surgeries are done that you choose the procedure with the highest base and add modifier 51 EX: 31267.50 31255.50 31276.50 31288.50; I would bill 31267.51

And, if two or more surgical procedures are done that share the same ASA code and are not components of one another than modifier 51 should be added EX: 54324 and 54161; I would bill 54321.51

We don't bill with modifier 50 here and I'm not sure why and I've never been explained why; however I can use 51 if the insurance recognize it.

51 Modifier Question