#english

Q: Sometimes we can omit the common auxiliary verb after and, sometimes we cannot, right?

A: Yes, it depends on whether the omitted part is still clearly understood and grammatically correct.

In your sentence:
✔ "Changes have been made and reviewed."
This works because "reviewed" logically shares the same "have been" from "have been made."

But in:
❌ "Changes have been made and are reviewed."
You cannot omit "are" because "reviewed" would then lack a clear verb.

A simple test: If both verbs logically share the same auxiliary verb, you can often omit the second instance. Otherwise, you need to keep it.