90%+ of the cars I've seen involved had aftermarket filters as well, I'd say none had ACD filters, but that's not true because one of the first Malibus I ever did hadn't even had it's first oil change.
Was the oil life at 0%, or was it not yet time for its first oil change?
I assume that car was built before the oil meeting 2nd Generation Dexos requirements was used in the factory?
Can you estimate how many you've personally worked on?
It seems like dozens of cars repaired would mean thousands of cars sold, but I have no idea how many Malibus and Cruzes your employer sells.
Was there any pattern to which piston failed first?
We had one member here who claimed that two out of two failed in his family
, using more than one quick lube shop and always with Dexos oil specified. Brand of quick lube wasn't mentioned.
I bought a jug of Pennzoil Platinum last month, it's first generation Dexos1, and SN, not SN Plus. I looked it up on Pennzoil's web site and the Platinum was reformulated in May 2018 to make it meet SN Plus, and mine was more than half a year old when I bought it. It seems like any Pennzoil linked oil franchise wouldn't have been able to supply good oil until this past summer.
I checked Valvoline, found a press release from early March 2018 claiming that Valvoline was the first to address LSPI and meet the not yet official SN Plus standard, but nothing to suggest any of their oils met that standard before March. At least Pennzoil recognizes old oil might be on the shelves and specifically tells us which products are safe. It's entirely possible that Valvoline Instant Oil change was using unsafe oil before 2018, even if you paid extra for synthetic.
My 2016 was built in May 2016, with dealer oil changes in February and November of 2017. I assume that it always had ACD 5W30 Dexos1Gen2 in it before this month (now has 0W20 M1 EP Dexos1Gen2 in it). The Gen2 oil was in the factories 2-3 months before my car was assembled, right?