Generally, yes. I know the rule explicitly says "the first sentence" only so another mod may feel differently.
I, however, remember the discussions among the staff that prompted the rule. Folks were cutting and pasting entire articles without attribution, sometimes trying to make it look like the words were their own. That had to stop. It mostly has.
OTOH, if you'd like us all to never exercise any judgement, allow no leeway, and rigidly enforce the rule, let me or any other staffer know.
I usually copy and paste a couple of sentences that pertain to the subject of the thread, and then copy and paste the source, so that others can get the full context of the article for themselves, then usually the rest of that post I offer up my conclusions or opinions of the articel.