My understanding - which could be wrong - is that the baseline impurity levels for oil in the can is for larger particulates than the filter. Hence the nuisance bypass pop out indications and hence the reason 'some' (no names, no pack drill) operators use pre-filtering. As mentioned in the report.
It would be nice to know why more attention wasn't given to the electrical power loss. Was it a sudden Nr drop or AC GEN overheat - caused by loss of cooling oil? I think it's also a bit simplistic to say the AC Generators are engine driven, too. They are essentially MGB driven, and most certainly MGB oil cooled.