Do Not Leave Motor Oil In Motor Beyond 12Months

Was that a "use by" date or a "best if used by" date?
I'm sure is was 'use by' because of the shorter text and less ink use, but the lawyers made them change it I would guess as it is now best if used by, at Kraft.
The Manual for my 2019 Jeep states never leave engine oil in beyond 12 months. I’m assuming Chrysler states this because the oil gets caustic an can be detrimental to some internal engine parts even if you have not maxed out on the oil’s mileage rating. Is this assumption correct.
If you're not driving a new vehicle enough in 12 months to require one oil change, you should probably sell it.

Time after time it has been shown that the calendar does not dictate OCIs, but the amount of driving and conditions of that driving.

Agree that the owner's manual is written for people that never do anything but put gas in.
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I change by mileage and not time. I changed the oil in both trucks earlier in the year and the oil had been in them for about two years. I last changed the oil in the Mustang in May of 2020.