In my mind, I always hear this analogy and I never come away satisfied. And I'm not saying there's anything wrong with changing a filter every time. I've always changed the filter every time myself. Except for recently on my son's RX8. We put a Purolator Pure One on it and because that rotary is ... how to say this ... more directly responsive to good maintenance, he and I change that car's earl every 3,000 miles. So this last time I said F-it (not to him, I don't generally cuss in front of my sons, unless a democrat), let's leave it on one more 3,000 mile interval. We both agreed.
I don't look at it like underwear. Because cycled earl flows through a filter and then magically - presto-change-o the earl comes out clean as a whistle. Ok, not really. But the earl filter removes a lot of dirt. It doesn't add dirt. It catches or passes. So if you change to new earl with the same filter, the crud that's in the filter doesn't get released into the new oil ... if it did, that is one crap filter. The crud stays in the filter, and new crud continues to collect.
Here's how I'm looking at it. If I'm mowing grass with my pooooosh mower (and bagging), and I stop to empty the mower's bag into a grass bag, I can fit 3 mower bags of clippings into 1 "grass & leaf" bag. Why would I dump 1 bag of grass into it, leave it 1/3rd full, and go get another grass & leaf bag?
Now, I'm only just speculating. I know very little. But I suspect a 50% used oil filter *might* filter oil BETTER than a brand new one. In my mind I suspect the crud in the filter to actually help catch additional crud. The drawback being that the flow rate through the filter is going to go down as more and more crud collects in it. But could that reduced flow rate lead to a problem? Dunno. Maybe. Especially if your Mirage engine is low on earl already.
Tis an interesting topic, this thinking about using a used earl filter for more than 1 o.c.i.
Grumpy - I got a good chuckle out of imagining you crawling back into your hole!
But ... stay out here with us!