That there may have been 18,000 invented gods, their being invented has no bearing on whether the 18,001st is also invented.
Let’s say I’ve been commissioned to pick up a friend of a friend, named Dana Smith from the airport whom I’ve never met. I have no idea what they look like. So I hold up a sign with their name prominently displayed on it and one right after another, people — both men and women — approach me claiming to be Dana Smith. One after another turn out to not be the Dana Smith I am there to retrieve. None of these frauds affect the probability of the next person in line being Dana Smith. They are each individuals who must be assessed on their own.
Likewise, 18,000 gods who are invented have nothing to do with the probability of a real God existing. They aren’t tied to one another and need to be investigated on their own, according to their own merits.
Sifting Reality 
I assume that the real Dana Smith provides Mesurable, Obseravable, Repeatable proof to me.
Obseravable, (photo ID, email about pick up ect.) Repeatable, (more then one ID) and meaurable (I could call a government body to confirm)
If I just accepted that this Dana Smith was the real one, when all those before or her also claim to be this person, and accepted merly on her word, then it almost does not matter that I happend to be right that one time, because why did I choose her? I was more likely to be wrong then I was to be right, and in the future if I make this decision using the same criteria I am likely to be wrong.
Cameron
I cant prove what I had for breakfast by your standards but I assure you I did eat.
But I think there are good legitimate reasons to believe God exists. You not being convinced by them is not the same as there being none.
The analogy I provided shows that each claimant to be Dana Smith needs to be addressed as individuals. Just because there have been imposters doesnt affect the probability of the next one in line being Dana Smith. Just like you cant assess the probability of the next number on a roulette wheel is based on what has already come up because each spin is unrelated to the previous one.
Cameron
One more thing since you mentioned a couple things. I would say God has shown his ID, Atheists however believe its a fake ID. It could have been a line of people named Dana Smith or it could have been a line of people with fake IDs. None of it is relevant to the point of probabilities I was making.
Let’s say the first 18000 Danas were lying. Merely claiming to be Dana Smith. It’s obvious that to lie and say you’re Dana Smith is very trendy, and has the obvious benefit of getting a free ride out of the deceit.
So, yes. It’s likely that you’ll run into one or two more fake Danas.
So, what?
I’m not Dana Smith. What does that say about Dana Smith’s existence?
But you do accept that the majority of god concepts are invented. By man. This is a historically demonstrable fact if you believe only one god can be true. Then you ask yourself why the invention of the other gods? Power, control, etc of man over other men?
Then, if you think critically, you might ask ‘Is mine invented?’. And why don’t others accept the truth as I do? After all, I’m a minority believing in my particular true god. Why won’t others believe us, and why are they so attached to their invented gods? And why are the numbers of believers in my true god falling year on year (except if you’re a Muslim)? Is the evidence I relied upon disappearing, or are people less reluctant to accept the evidence I did? Or maybe Islam is true because more people are accepting that evidence (albeit it’s very difficult to leave that religion)?
And once you answer all these questions… you’ll be back where you started. Certain that you and your minority group of believers know how the universe started, how to live and how it will all end.
Personally I do think they are the imventions of prior generations. Your directive back at me though implies there is the same quality and quantity of evidence for my God claims as any other religion, which isnt true and is why I posted the recent challenge to atheists. Too many atheists make this erroneous claim which is just false. It may be the case that my religious target doesnt exist, but it stands on better evidences than Hindus Mormons and Muslims deities.
Where do you think they came from then? They are either 1) True 2) Not true. If you don’t believe them to be true, then they must be (not supernaturally) created to appear as true. Then they must have been (at some time) man made as no other natural entity is sophisticated enough to create such a thing.
You’d have a much more fruitful discussion discussing the relative evidence of god / allah with a Muslim. They would be as staunch as you are in their own favour. However, and because I’m a sucker, what is the single best piece of evidence you think exists for the Christian god?