Well I am ashamed to say I have yet to finish this one, and am starting to tire, especially with 4029 burning a hole in my pocket (no pun intended).
I have the 36 digits, the 3x3 key, the 3 additional double digits, and four clues that I have answers for that do not match the answers length.
Unfortunately my letters for the intersections around the "special" cells do not seem to easily mesh, but I am adamant that all four answers are correct! So, I am four crucial grid insertions short and cannot make the final play.
Hence, I am struggling, have enjoyed it immensely though and as others have said when the theme became clear it was a great feeling.
My solves of the four consist of a simple anagram with a clever definition, two pleasing cryptic definitons, and a straight forward "do exactly as it says" clue.
Have been thinking about the title but beyond what others have aired haven't cracked it yet.