The answer is blindingly obvious.

[Tank]

If holy books are true then all gods are real.

If a person thinks their holy book is the only valid holy book then they are guilty of the logical fallacy of special pleading as there is no evidence that one holy book is better than another.

If holy books are not true then no gods are real.

So which is it?
Are all holy books true?
Is one holy book true (take your random pick of which one).
Or are no holy books true?

The answer is blindingly obvious.

[Asmodean]

Well... The TL;DR answer is, "It depends."

"True" in this sense is a matter of degrees rather than a logical statement, and so we tend to use words like "factual" or "non-fiction."

The reason for that, I imagine, is that it speaks more to the work's intent, context and content than a binary true/false check. A non-fiction book may contain falsehoods, though not lies. Even its premises may be false, or may eventually be shown to be so. Or they can be true or eventually shown to be true. That does not make the book itself true or false, however. It may make it more or less factually accurate, as viewed through the lens of your standing model of reality.

Are all holy books factual? No. Do some holy books have factual elements? Yes. Are those elements true? Perhaps. Perhaps not. Ask an historian.

As alluded to above, I do understand that you could use "true" in a broader sense, but in this case, you seem to be using it in conjunction with if-then statements, which indirectly assumes using it as a logical test. (Your conclusion of which is flawed, by the way, but I see what you were trying to do, so I'm happy to leave it be)

So,
Are all factual statements in all holy books accurate? (On a passed check, this is the closest you come to "All holy books are true")
Are all factual statements in some holy books accurate?
Are some factual statements in all holy books accurate?
Are some factual statements in some holy books accurate?
Are no factual statements in all holy books accurate?
Are no factual statements in some holy books accurate?

There is another option for each with no holy books, but I omitted that one as the inevitable else case.

You see, there is quite a lot more to this than the simple test you propose, and that reality will not be lost on the more sophisticated believer. As for those who wouldn't even care to consider such possibilities - you are unlikely to convince them, if for no other reason, because they are unlikely to listen and/or understand and/or give a toss.

Still, The Asmo approves of mental exercises, so if no-one else, He, at least, is happy to come play.

[billy rubin]

. . .  as there is no evidence that one holy book is better than another.

^^^thats a universal negative categorical proposition.

to assert that it results in a true conclusion in a sound argument it must first be demonstrated to be true.

how would one do that?

[Tank]

. . .  as there is no evidence that one holy book is better than another.

^^^thats a universal negative categorical proposition.

to assert that it results in a true conclusion in a sound argument it must first be demonstrated to be true.

how would one do that?

Good question. How would you do it?

[Asmodean]

By first figuring out what it is specifically you are testing, then... Testing it?

Is there evidence that some holy books are more eloquently written than others?
Is there evidence that some holy books are more historically accurate than others?
Is there evidence that some holy books are more broadly factually accurate than others?
Is there evidence that some holy books are more popular than others?
Is there evidence that some holy books are more interesting than others?

Any combination of the above and a lot more besides may constitute "better." Any of the above is testable.

[zorkan]

Are all holy books true?
Is one holy book true (take your random pick of which one).
Or are no holy books true?

The Book of Zorka is without doubt true IMO.
You see, it's a matter of opinion.
But can you afford to doubt it?

Ref. Chapter 4 - Last Days.
"At the end of time the earth will be set ablaze.
Only Zorkans will escape to another world.
For the rest it will be nothing but wailing and gnashing of teeth."

[Tank]

 

[Asmodean]

The Gray Tome is fare more factually accurate though.

The Asmo giveth and The Asmo taketh awayeth. Mostly taketh awayeth, but sometimes giveth, though there is little evidenceth of him givething. Never you mindeth that. And lo, when The Asmo taketh awayeth for the final timeth, then there will be nothing lefteth. As His Divine Will dwindleth, so shall the Universe dieth for evereth and evereth.

[billy rubin]

the way to do it is to test their histories, their predictions, and tbe reality of their doctrines, and then compare.

i think they all generally fail at history, and i have found prophecy is usually arguable.

so the reality is where the most straightforward test would be.

the simplest way to test it is to meet the gods, in an unambiguous manner. i dont know anybody who has, although i have heard some very convincing testimonies.

[Recusant]

Coming at the same challenge from a slightly different angle, which holy book has produced the least harm? 

Not really relevant but that would be the "better" volume in my opinion. Doesn't make the book "better" from the perspective of validating its assertions regarding deities though.

As far as I am aware none of the pertinent* assertions regarding deities have been unequivocally validated in any holy book. Some may attempt arguing a case claiming validation. However, argument/apologia never escape equivocation; it's in the nature of the endeavor. Inevitably there will be special pleading.

*To the question of existence of a deity or deities.

Where true = showing that a deity or deities exist then I agree with your conclusion Tank.

[Tank]

It really is the case that no deistic/theistic claim has not been substantiated.

[zorkan]

The Gray Tome is fare more factually accurate though.

The Asmo giveth and The Asmo taketh awayeth. Mostly taketh awayeth, but sometimes giveth, though there is little evidenceth of him givething. Never you mindeth that. And lo, when The Asmo taketh awayeth for the final timeth, then there will be nothing lefteth. As His Divine Will dwindleth, so shall the Universe dieth for evereth and evereth.

Which version are you quoting from.
The new or the revised?

[zorkan]

Coming at the same challenge from a slightly different angle, which holy book has produced the least harm?

The Book of Zorka has never done any harm in this world, despite Zorkanism being the galactic religion.
Them aliens up there in our airspace are missionaries trying their best to promote it, but we don't listen because we have evolved our own gods.

[Asmodean]

Which version are you quoting from.
The new or the revised?

There is only one The Asmo, who is The Asmoest among all The Asmos, and His is the only True Gray Tome.

It really is the case that no deistic/theistic claim has not been substantiated.

They tend to fall flat at the "because God" stage. Often, even before that. That is not to say, however, that none of their claims may hold their liquids.

[Old Seer]

Question: If one were to say that their God is the total of nature, does his/her god exist.