Lightning to 3.5 mm adapters only for “iOS 10.2 and below” I’ve seen quite a few Lightning to 3.5 mm headphone jack adapters that only claim compatibility with iOS 10.2 or lower. I found that very strange, since I generally expect my adapters to keep working even after I update an OS. 

What does the iOS version have to do with a simple adapter like this? Does an obvious reason exist for why sellers make this claim?
Apple has had a Made for iSomething (MFi) program since 2005, though initially it wasn't strictly enforced.

Anecdotally, because I can't find any announcement, only user complaints - ref Reddit: [Request] Tweak to enable non Mfi chargers on ios 10.2 &amp; others - with the introduction of iOS 10.2 the requirements became more stringent.

MFi cables &amp; devices require a certification chip in them, licensed from Apple, otherwise they will be rejected by the iDevice.

The implication for cables being sold as 'works up to iOS 10.2' is that these are inferior cables - they are certainly chipless.
It's probably impossible to determine at such remove whether they were of sufficient quality to become certified, but made before the chip became compulsory &amp; are now simply old stock, or whether they are just cheap knock-offs that would never gain certification.

Certification doesn't seem to be that difficult or expensive [It's been described as a 'tax', being a percentage of sale price] &amp; I doubt anyone would even bother to make non-certified cables these days, as they would just be returned by any customer using a recent iOS.

I found a good blog about it on HowToGeek: What Does Apple MFi-Certified Mean?