This polymerization process can happen rather quickly.I agree with the above. Something doesn’t add up. It was very low and it sludged up.
Let's say a small amount of glycol leaked into the oil from a head gasket problem. or a third party additive or a vegetable oil was used which caused a lump of gelled material to form in the pan.
The polymerization process accelerates under heat and oxidation and the lump grows. So how did it grow? It kept gathering its material from the bulk oil in the engine, reducing the oil volume over time, so when checked, it would be low.
I saw this once in an OTR Truck fleet. Every time a unit came in, the oil was checked and "topped" off, while all the time this cancer was growing in the sump and wasn't found until, at the next oil change, when the oil came out in lumps and the sump pan was removed to determine why.
Some of the causes were attributed to aftermarket additives added by the truck drivers themselves, and some were head gasket leaks--glycol intrusion.