Yes, you too have a lot to unpack here.

Who is this monolithic "they" you speak of? Philosophers?
A. Yes, basically anyone that works with that prescribed usage.

Belief is a choice, you say.
A. Yes, fundamentally. Belief is simply the subjective decision that a person makes to hold information as true. Disbelief the opposite: indication to hold information as false.

Belief has 2 connotations for you: you say.
A. I think fundamentally in agreement with you, but I might would give a little more semantic detail if I wanted to technically cover the full aspects. For now, I won't go into exhaustive explination. But copy here my brief last statement of my O.P.
B. The information held as true or false(belief/disbelief) could be verified as true or false regardless of how the person holds the information in mind.

As to some name changes, or classification changes like your example of homosexuality changed from mental illness:, these name or classification changes does not change what it is.

Pluto is or is not a planet: as to "truth", Pluto is pluto, What if an asteroid were to obliterate pluto and it is just scattered debris. Then it's no longer a planet for sure. So, things can change and the "truth" of it being what it was changes too.

Another example of name changing and word evolution is the word religion. As you use:

"There is a god" opens the philosophy of religion for example.

For 2000 years almost, it has been documented that religion is simply helping widows and orphans in need while avoiding worldly corruption.

A spaghetti monster is not required to do religion.

Religion ... pure and faultless is this: to help widows and orphans in need and avoiding worldly corruption. James 1:27

Semantics and logic are intrinsic ... all I have time for at the moment.

Just before he died Socrates asked his friend Crito to go and sacrifice a cockerel as was the custom at the time when recovering from an illness. However, I am not inclined to think that Socrates regarded life as an “illness” from which death is the recovery.

@Word well to speak plain English, truth is not something that is always static. Belief is always a choice.

@Word also, as per homosexuality changing, yes the changes in the DSM did change how it is viewed. It is no longer a diagnosis of mental illness. So one cannot be diagnosed as being mentally ill just for being gay, so it did change for many reasons.

This means there is a legally and medicinally accepted new truth of gay being normal. As it should be.

So truth in this instance, very much did change. I am glad too!

@ClareCK not as a dispute as to how legal or medical should or should not view homosexuality. But, just because it is called illness or normal is not what I would consider that truth is about. Truth -
the quality or state of being true. What is being true? True - in accordance with fact or reality, accurate or exact.

Normal
the usual, average, or typical state or condition.

Such can change:
the new normal — a previously unfamiliar or atypical situation that has become standard, usual, or expected.

How something is classified for standard doesn't change what it is. Legal, medical, political is just changing the standard of accepting it as an allowed standard. It does not change what we refer to as homosexuality. As to say, homosexuality in it strictest view in homo sapiens has 0 (zero) evolutionary fitness. Evolutionary fitness pertaining to the amount of offspring. Homosexuality, wheither legally, medically, politically acceptable or not does not change the fact that homosexuality in its strictest sense in homo sapiens produces no offspring to pass on genetic information to a next generation.

You don't think it true that someone would know they got hit by a bat?

@Word I think it presumptuous that the bat is one used in baseball. One could be hit with a flying rodent like creature. In fact, it would be easier to imagine that they weren't unconscious after being hit with a vampire bat, for instance.

@rainmanjr I did mention baseball as the type of bat.

@Word So you did. I should reread instead of trying to be witty. I can't imagine being hit with a bat and don't really want to so I can't guess. I tend to think that they would know.

@rainmanjr ok, nothing wrong with being a little witty at times, just so long as you don't go bat crazy.

@Word Let's do the theme song. Nah nah nah nah nah nah nah nah nah nah nahna na. BATMAN!

The people I come across making the statement I said they said.

Philosophical knowledge is saying information in mind can only be called "knowledge " when it is in fact truth.

I point out, knowledge is information in mind regardless of truth. Verfied information of the knowledge in mind can be found to be true or false.

From website example they use:

Most epistemologists have found it overwhelmingly plausible that what is false cannot be known. For example, Hillary Clinton did not win the 2016 US Presidential election. Consequently, nobody knows that Hillary Clinton won the election. One can only know things that are true.

So when we say that only true things can be known, we’re not (yet) saying anything about how anyone can access the truth. As we’ll see, the other conditions have important roles to play here. Knowledge is a kind of relationship with the truth—to know something is to have a certain kind of access to a fact.[3]

[plato.stanford.edu]

Here's the problem I have with the epistemologists statement.

It can be known that the information (or statement) is false, "Hillary Clinton won the election "

So, I can know false information and know it to be false.

@Word There can be knowledge also, that is not known to some, but known to others. So it doesn't have to exist in everyone's mind to be true either. What would you call that? Esoteric knowledge for example is like when people in certain professions know information other don't. So knowledge can be out there, but unknown to some.