Well, I don't know about these 8 countrymen of yours whose employment based AOS process was completed between 7.5 to 8 months, However USCIS's
Historical National Average Processing Time which I prefer to go by shows average processing time of employment based AOS is way over the average processing time as reported by your friends.
FY2015 - 6.5 months
FY2016 - 6.8 months
FY2017 - 8.4 months
FY2018 - 11.1 months
FY2019 (UP TO 3/312019) - 12.3 months
Maybe theirs are outliers, maybe their FOs weren't some of those busy ones, I don't know. One thing I do know for a fact is that most DV based AOSers chargeable to Iran typically wait a while, (longer than fellow AOSers) before getting their approval. Only a few of them have succeeded in completing the process within the "normal" time frame as other DV based AOSers. And before the travel ban came into effect, those processing CP equally ended up in several months of AP by the way.