Accessibility is a continuum
The sooner you realize accessibility work is never done, the better off you'll be.
No one is ever done with accessibility. Realizing that is a step on the path to Enlightenment!
This is what I said to a lead engineer in a discussion about the remediation of the dozens of defects found in a 3rd party accessibility audit. He was giving me a status update, and said "For what it's worth, I don't think we'll ever be done with accessibility work, but we aspire to get close".
Accessibility is a continuum. It's not one of those "done and dusted" kind of thing.
First, you always develop new features. Second, assistive technologies change. And third, WCAG is the starting line, not the target!
New features
Most organizations creating a product are on a constant development path. This feels like one of these things that I shouldn't have to say. It's a concept everyone knows. I say it nonetheless because it needs to be real clear: Everything an organization builds has to be accessible. And if the organization hasn't focused on accessibility in the past, once they are aware of the need and importance of accessibility, they really should ensure everything new they build is accessible! From that perspective, you're never done with accessibility. You may remediate all the items your 3rd party accessibility auditors found on that "one point in time" audit. But that's just a snapshot of your site or application.
Technology changes
Browsers and assistive technologies (AT) are also evolving, just like your product is evolving. Most of the time, the technology is improving. Getting more clever. Sometimes, conflicts happen between the browser changes and the AT changes. Things we used to do one way, often as a work around, have to be done a different way.
WCAG is starting point of accessibility
I've said it before. I'll say it again. Plenty of other accessibility professionals also say it.
The Web Content Accessibility Guidelines (WCAG) are just guidance to get started. They don't encompass all of accessibility needs. It's just not possible to cover all accessibility in one set of guidelines. The same is true with accessibility regulations for the built environment.
The guidelines are what a group of expert came together and created. It is not perfect. It is not complete. There's a reason the guidelines are evolving.
The digital accessibility community agrees: there are two main groups under covered by WCAG. Folks with low vision, and folks with cognitive impairments. But they aren't the only groups who's needs aren't covered.
AA vs AAA
And then there's the fact that we often work towards WCAG Level AA conformance, when so many elements of Level AAA would make a massive difference to many people. Criteria that are staying at Level AAA only because the working group can't reach consensus.
So, yeah!
Organizations that think they can “do accessibility", as a one big push, and then be done with it… These organizations will suffer in the long run.
Change your perceptions of accessibility. Change your internal culture and start looking at the work you do as one of “inclusion”, rather than one of “checkbox WCAG conformance”. You'll be much better off for it. I guarantee you.