The "se" at the end of letter groups seems to appear too often to be actual letters or a letter. I'm guessing it's a pointer toward a key to be used to decipher the letters that go before in the group. Same for "te". So he has a couple or a few keys he applies to groups of letters. Similarly, the n appears too often and in odd places in strings to actually be a letter. It's also written unusually. So I'm guessing it's part of the code -- maybe negating or reversing the key from time to time. I saw a comment suggesting pg 1 is a recipe. That would explain all the repetition. Pg 1 also looks a bit like a computer program. I think this will turn out to be a simple but slightly irrational code, which is why the experts are stumped. The keys might be hidden on the "Notes" page to help remind him, though if he's been using them for many years he may have them in his head. First line in third group on Notes pg is interesting, almost symmetrical around the "2", with broken symmetry making "nmnl" "cbrnse" "wsr" and "pte" look like words.
