In English grammar, we have "3rd conditional clause" with the format of:
(modal verbs) have been+ IF past participle
- Ex.If I had known you earlier, I could have hired you.
HOWEVER, there are some instances that English language users, mostly the advanced ones, mixed this up.
(modal verbs) have been+ Simple past
- Ex. I am mad now, because my account was the one that was charged for the processing fee when it should have been my buyer.
This is appropriate I think, but is this beyond the grammar rule? And only applies to spoken English?