You can meet every standard in the document and still be impossible to deal with.
Compliance is a floor. Somebody else set the height of it, a while back, based on what seemed reasonable to ask of an average organisation at the time. It is a useful floor and I would not want to work without one. It is also not a description of whether anybody can actually use the thing you have built.
What the standard is for
A standard exists to prevent the worst outcome, not to produce the best one. It has to be checkable by someone who has never seen your organisation, which means it has to be about the artefact rather than the experience. Can the text be read aloud by software. Is the gradient right. Is an alternative format available on request.
Good questions, all of them. All answerable without anyone ever having reached the end of the process.
Where the gap opens
The gap opens in the joins.
Every step in an enrolment can pass its own check and the sequence can still be unusable. The form is accessible. The confirmation email is accessible. The portal is accessible. But the form asks for a document that only arrives by post, and the portal times out in eight minutes, and the confirmation goes to an address that cannot be changed without ringing the office.
Compliance is measured one component at a time. People use the whole chain.
We are compliant, and she can enrol without ringing up to explain herself, are two different sentences, and only one of them is about a person.
The phone call is the tell
Every process has an exception path. Ring this number. Ask for the alternative format. Speak to the team and we will sort it out for you.
The exception path is where an organisation hides the cost of a design it did not want to change. On paper it looks generous... there is always somebody available to help. In practice it means one particular group has to make a phone call, in business hours, and disclose something about themselves to a stranger, in order to do what everyone else does in a browser at eleven at night.
That is a charge. It gets paid in time, and in the ongoing small work of explaining yourself to people who did not need to know. Nobody inside the organisation ever sees the charge, because it appears in no budget line anywhere, and the person who paid it usually says thank you at the end of the call.
What to measure instead
Count those calls. Not as a service statistic, as a defect list. Each one is somebody telling you exactly where the process broke, for free.
Then stop asking whether you meet the standard and start asking who finished. Take the whole task, start to end, in the worst realistic conditions. Old phone, bad reception, no printer, no support worker that day, one go at it between other things. See how far you get before you would have given up.
You will find the drop-out point quickly. It is usually one screen, or one document nobody can produce, or one sentence in a letter.
And when you find it, stop calling it non-engagement.