See my in-depth post above with cited sources and transcribed dialogue. Go figure.
I did. Not a definition to be found on any of those sites. I'd been to a couple of those before, notably the RC Tonewoods site. The mandoweb site description (not a definition) is great in that it makes fun of the whole concept of sinker mahogany. "[W]ood that is alleged to have been submerged many scores of fathoms below the surface of the river where, under more pressure than a sophomore with a statistics test tomorrow morning it becomes “as one” with the environment to which it was subject and its molecules compressed like a stack of five (5) IHOP pancakes under a 4-ton steamroller." It gets funnier from there and they manage to work in the 1953 movie Shane and White Castle hamburgers. I read "many scores of fathoms" and was thinking "WTF?" but as I read on I realized they were basically saying, here's the story on this wood but it's a load of crap.
The RC Tonewoods site is notable in that comparing that site to one you didn't list, the Huss & Dalton guitars site, I'm fairly certain RC supplied H&D with their "sinker mahogany" (The H&D wording is straight off the RC site and H&D attributes it to their supplier). The interesting thing about that is the H&D site has photos supposedly showing the trees being recovered from the river in Belize. The photos do not show sunken logs but rather trees that have blown or fallen over into the river and are only partly submerged, partly still on the riverbank. The parts that are under water are just barely so and during the dry season in Belize are probably not at all.
The Hearne Hardwoods site claims to have coined a new phrase, "We are calling it "Sinker Belizean Mahogany"...." and then goes on to repeat the same stuff as RC and H&D about British Colonies and small boats and pulleys which makes a great sales pitch but none of it has anything to do with the actual wood in question. Lumber Jocks spins yet another bit of nonsense. First, they say the locals were given permission to harvest this lumber from the river (so the trees were growing in the river?). Then they go on to make this amazing claim that really isn't a claim but they know some folks will always see what they want to see, "I’ve seen the logging maps from the British that were taking this lumber back to Europe in the 17-1800’s, so you can almost find out where it came from. Who knows how old it was when it was logged." Clever sales pitch. They don't make any actual claim about the provenance of the wood at all but they throw out a bunch of nonsense and let the buyer's mind fill in his own details. The Dog Trot site doesn't mention mahogany at all, only "sinker oak" and "sinker cypress". I found "sinker cypress" really funny. A tree that grows in water in a swamp is considered "sinker" if it falls over?
As for the Wildwood video, paraphrasing is not quoting. We do not know how much time passed between David's conversation with Paul, which happened the last time they "visited Wildwood together", and the time the videos were made, which we know was at least enough time for Wildwood to decide on the specs of those guitars and for the Private Stock team to build all twenty of them. Who else did David talk to about "sinker" wood during those several months? Did he mix any information sources up? That IS A SALES VIDEO so of course he's going to make it sound as cool and authoritative as possible. What better source to attribute the info to than the man himself? I am old enough to know that when two respectable people say different things about the same thing there is usually an innocent mistake in there somewhere and you will never know what it is until those two sit in front of you and explain it.
Now let me get to my point. I kept asking you to give me a definition of sinker mahogany. You never did. It was a trick question or sorts. There is no definition of sinker mahogany. It is a made-up BS term used by salesmen to sell wood. Anyone one can have his or her own definition of it and they are all correct and all wrong. What is it? Wood that got wet? In a river, in a lake, in the ocean, in the rain? Fully submerged or partly? For how long, 30 seconds, 30 years, 300 years? What does it take? Fresh water or salt water? How deep, 1 foot, 100 feet, 1000 feet, many scores of fathoms? (FYI, only ten score of fathoms is 1200 feet and is 50% deeper than the deepest river on the planet, the Congo. A bit beyond small boats and pulleys to recover I think.) Now let me speculate for a second (my speculation is every bit as worthless as anyone else's and this thread has been full of nothing but speculation), maybe Paul Smith told David Grissom exactly, word for word, what David said in that video but then Paul did some research, realized "sinker mahogany" could be anything you wanted it to be so he came up with what he called "sinker" mahogany. Perfectly legitimate.
Now for my final words in this thread. (You're welcome ) Paul Smith could have made a video that said, "All the wood used in these guitar necks came from mahogany trees cut in 1855 that spent 155 years on the bottom of a river, was recovered in 2010 and sold to us." No customer could have ever proven him wrong and that would have made a tidy ending for the story. He didn't say anything like that. Because he didn't try to make any elegant cover up that would have made some un-informed consumers happy, I believe his explanation. I will continue to believe it until someone offers proof, not speculation, not heresay and not outright BS, to the contrary. At that time, should it ever occur, all I will have to say is, "So what? I knew before I bought that sinker wood is just sales BS and doesn't mean anything. I mean, come on, don't tell me some doofus put any stock in that term without checking it out first."