In a 3 stage setup the first filter is oversized ("mud" filter as referred to by many) and is considered a polishing filter by us neophytes.
BTW - 100,000 s of diesel "mud" filter arrangements sold per year work quite well on all sorts of industrial engines. As with all diesels, and noted by many on this Forum, the bypassed fuel around the engine gets continually filtered or polished. That is all DIY polishing with its myriad of hoses, fittings and pumps is - just filtering. If you are worried about a bunch of crud in your tanks, two big spin on filters side by side work wonders. It certainly does for Cat where up to 200 gph can be consumed by an engine.