Running out an OCI a little long is OK AS LONG AS EVERYTHING ELSE IS OK. 26K is way too long without a lot of monitoring and UOA's plus filter changes.
A longer-than-factory OCI means you need to check your oil often for level, water intrusion, gas smell, soot thickening and/or sudden color change.
Really everyone should be doing this anyway, but if you have a short OCI you can get away with not bothering to check, since you're going to see the oil's condition soon enough on the next change. In essence you are changing your oil often just to look at it. That is what a dipstick is for.
Short OCI's are fully justifiable on engines with known issues like coolant or gas contamination or sludging, antique engines with no PCV, also severe service like towing, plowing or racing, excessive heat climates, and short-tripping. Another would be a low-usage vehicle, I change oil once per year no matter what the mileage.
Otherwise short OCI's are a feel-good waste of time and money, but at least the oil gets recycled, so it's hard to call it a waste of natural resources.
Note, I am not a fan of really long (>10K) OCI's on engines that are not made for it (like a Caddy or Vette with their huge oil capacity and filtration). I don't see the point of a paying for an UOA to run a typical engine past 10K miles since the UOA cost is similar to that of a oil change.
My personal comfort level for a good healthy modern engine is: MFG OCI in warranty, 6K-8K on synthetic for standard oil capacity engines out of warranty. If I really felt a need for a 3-4K OCI, I would also strongly consider an engine rebuild or replacement, because something is wrong that it needs new oil so often.
(I get beat up on by the short-OCI guys for whatever, and the long-OCI guys for wasting synthetic with sub-10K changes. I figure as long as the clamor is about equal on both extremes, I'm OK!)
