Despite bugs obviously getting fixed thereafter. So at most I got all updates to the same minor rev, not major rev. AD 17.1.9 released in November does NOT work for me. I'm not sure if it's because it's a hotfix rev, or if it's because there's some grace period. AD 17.0.11 was released Feb 28, and that version works for me.

EDIT I did test this just now using a license that expired Feb 24 2017. Off-subscription forum users might simply not be getting the time of day. I have half a mind to think that the update-without-license-issue exists by survivor bias: the only people they hear from are people for whom it's not an issue. A maybe more interesting point is that they stop taking your support emails the moment your subscription lapses. If all you're interested in is new feature updates, it's absolutely the case that your subscription pays out exactly one day a year. Mostly just minor fixes, especially to the newly released features that have never yet seen production use.

In a much more relevant way, nothing interesting or worth paying extra money for is expected to happen over the duration of that 21.x major rev you already did get a whiff of.

Altium subscription price