emika, I understand that telling them makes it easier (certainly for them) and this is why I generally do the same. (Please don't assume that I am anything other than gracious to the airline crew.)

I am asking whether anyone is aware of the airline informing deaf passengers of the duty to do this. To me, the bottom line is that my "failure" to do it is only a failure if I had been given this duty prior to being expected to perform it.

At the gate, agreed that they may not know what I look like. (In this particular case, this is a regular flight I take and they always act like they recognize me. They have found me in the crowd on other occasions and even signed thank you, and that kind of thing. But let's say they don't know who I am.) Does the airline NEED to know what the deaf passenger looks like to fulfill the one thing they need to do, which is to ensure the deaf passenger boards the aircraft?

First, they don't know which person it is, but they know there is A deaf person awaiting this flight. Maybe the person is still in the lounge. Maybe the person is at the duty free. Maybe the person is held up in security queues. As a deaf person, MUST I "sit right over there" or am I not permitted to browse the shops and snack bars like anyone else? The flight has been delayed and no new time has been announced. I can't go for a walk to stretch my legs? In fact, as I mentioned, I was in the bathroom when they moved, and therefore they would not have been able to notify me based on recognizing me in the gate lounge. (That also gives you an idea how quickly they moved.) As they collect the passengers in a herd to move to the new gate, they could glance at the facial expressions for someone who looks possibly confused by what is going on, and ask to see the Boarding Pass to confirm who it is.

Even if they do not know what the deaf passenger looks like, I think they can keep in mind a deaf person is expected and take one last glance around before they close the flight, particularly if that is the name that has not checked in. And if they move gates, they can ensure that there is some type of visual informational message left at the gate.

The gate had a video monitor, but it was not used to display the new gate location. There was no new flight number posted. It was just a generic "welcome to City X" message. The new gate was only displayed on a Departures board that would not normally be passed again after arriving at the gate.
The airline has an app, but did not put the gate in the app.
The airline has my text number, but did not text me.
The airline has the text number of my Next of Kin at home and has used it previously for other cancellations and rebookings, but did not contact it.
The airport has free wifi and charging stations near the gate, so it has provided the telecommunication support to ensure passengers are able to use this technology.

Everyone may not have access to their email and texts, but my argument is that the airline has a duty to use ALL of the technologies available to them, and not to rely on ONE SINGLE method, consisting of "the passenger shall self-identify at the gate", and then NOT TELL THE PASSENGER of this expectation.

I agree with you that if I self-identify once I do arrive at the gate, I have the means to increase their ability to recognize me, but remember, I have no guarantee they will remember my appearance or pass that information along to the next agent when they swap positions.

Clearly, the airline has ASSUMED that we will all do this. I think that is as faulty an assumption as assuming people can hear as well as they speak. Like your HoH friends, I do speak, and aside from this gate-moving disruption, I very frequently have encounters where the airline personnel are cavalier about notifying me even though I have self-identified at the gate.

There are pitfalls to promptly notifying the person at the gate. I may go to a great deal of effort to notify someone who looks "airline-y" but is, in fact, the delivery person from duty free, or the wheelchair porter, or an aircraft groomer or baggage assistant. Because I don't know how they organize their work and deploy their personnel, it is not my duty to second-guess their procedures and improvise additional steps and processes that may or may not be effective.

So, both the passenger and the airline have things they can do to increase the chance of the deaf passenger boarding the correct flight. However, it seems to me the airline has a DUTY under the ADA and more knowledge of the procedures they will use to ensure they board all of the checked-in passengers, whereas the passenger only has the duties the airline gives to the passenger as part of the transaction to buy and sell the ticket. I have performed every duty they have asked, in regards to self-identifying, and my assumption must be, if they have not asked me for more, then they are confident that their systems are adequate in all other respects.

My question, again, is has anyone ever been explicitly told they have the duty to self-identify at the gate?