An agent wants to see my narrative nonfiction book proposal. Do I state in the cover letter that six commercial houses turned down an earlier, much different, version some time ago? Or do I reveal this later if the agent likes the proposal and writes or calls? I don't want to jeopardize my chances right away, but I also don't want to seem less than candid, either. And, if I address the proposal's history in the cover letter, should I mention the houses, the editors, and any details? Some of editors who turned it down, for example, said that the story was intriguing but might be a hard sell.
Ah yes, the excruciating dilemma of when to tell how much. You've got some wiggle room here cause it sounds like only publishers turned down the alpha version and no one has seen the new and improved buy it now beta version.
It's also not a sin to learn from your experiences and apply that hard won knowledge. Agents want good material first and foremost so if you've rewritten and revised and are now faster stronger better, that's a good thing.
So, when to reveal the stitches? I'm going to vote for not on the first date. This is not some sort of law of nature, this is just a strategy.
I think you should write a compelling cover letter and query for the work as it is now. Snag the agent's attention. IF you get some interest, you should reveal that an earlier, less spiffy version was turned down by six publishers. Frequently agents can get projects accepted that authors over the transom cannot. Same project, just more oomph behind it. You didn't mention if you'd been agented on the earlier submissions. If you WERE, that has to be revealed up front.
You don't need to air your dirty laundry front and center but when the time comes you gotta mention your Sunday go to meetin' suit has been seen before.