Great recordings, LCB. I think the wood knocks always have meaning. My gut feeling is that there could certainly be patterns to them, but that those patterns may not be universal; that each BF (or BF group?) may use them in their own unique way.
Like some others here, I once had a wood-knocking conversation with a BF. I knocked first, three times, and they knocked back (but I think only once - I have to check my notes on that). I knocked three times again, and there was silence. I then realized I had probably overstepped and gotten a little too greedy, so I verbally thanked them and told them I would stop torturing them with my wood knocks -- and I got a final knock out of them!
I believe that final knock was meant to be an acknowledgment of my thanks, as well as an expression of appreciation that I had decided to cease and desist.
IMO, there was no specific information in those particular knocks, beyond what I've just described. I think the BF was basically simply expressing a willingness to engage. The knocks meant mostly, "I hear you, and I understand what you're saying." But I think the knocks had such limited meaning in that context because they knew I wasn't capable of getting any additional meaning out of them. I think that, if they had been communicating with each other in that moment, instead of with me, the knocks would (perhaps) have carried a lot more meaning.
This famous passage from "Through the Looking Glass" is about words and their flexibility, but maybe someday we'll find out that the same idea applies to wood knocks, too:
"‘When I use a word,' Humpty Dumpty said, in rather a scornful tone, ‘it means just what I choose it to mean—neither more nor less.'
‘The question is,' said Alice, ‘whether you can make words mean so many different things."
‘The question is,' said Humpty Dumpty, ‘which is to be master—that's all.'"