This drastically reduces the keyspace, making brute-force search more intelligent and focused.
Drastically? Did you try to calculate how "drastically" it is? I think the better word is "negligible", not to mention this approach has no solid grounds for this.
“No private keys have triples, repeated double pairs, or double 6/9/a/d — filtered to match historical puzzle patterns.”
It does not mean anything at all regarding the unsolved private keys.
For example, none of the puzzles before 69 had "101" as the prefix, so following your logic the puzzle 69 could not have "101" as prefix, but it did.