4. Thus, I assumed the above 'being' might be left out but wasn't sure. With your pointing out now I've come to think this 'being' is needed even in an abbreviated subordinate clause, since the conjunctions like before, after aren't included in the list of above rule - a pronoun subject and the verb be can often be dropped.
Yes, Deepcosmos, "being" is needed in all such sentences, even though you are able to find examples of incorrect uses of English on the Internet. The three examples you quote are incorrect. "Before" and "after" are never conjunctions, even when they are complemented by finite clauses. They are prepositions.