This is an expression that gets up my nose big time I don't wish to be disrespectful because I know it's commonplace and Bernd uses it. Bernd is one of the finest and best thinking anglers I know. So this FP is about offering an alternative viewpoint... for Bernd.
Cracking the code for me would mean that you solve the puzzle. You go from zero to one. That's the solution. Having solved it it's time to move on. That's not how I see any aspect of fly fishing.
For me fly fishing is like a huge complex jigsaw puzzle. Every day that you fish you learn a new piece. Sometimes it's a similar piece, maybe it's even the same bloody piece. Sometimes it's an edge or even a corner. At other times it's a piece of sky. Occasioinally you discover a piece that only fits by shuffling or reversing previous pieces. Every once in a while you're forced to add another dimension.
Only after you have very many connecting pieces can you get an idea of what the general puzzle looks like. That may be "cracking the code" for some, but that is certainly not having cracked the puzzle for me! For the puzzle is far more complex... and the deeper you go the more pieces you find, for you will never completely learn any aspect of flyfishing - even if you live forever. You might learn 90% of a type of fly fishing and then be on diminishing returns because the pieces become tiny (and most of them are sky!). It must be so, because we are always learning - as of course are the fish too...
After - let's say 3000 days of fly fishing, fishing the same type of fishing, you should certainly have learned most of it and be by this time what most would regard as an "expert" in that particular field. Then you can develop your expertise further - or change the puzzle to a new fish or fishing type.
Solving (most of) one puzzle can help in another but I don't see much in the way of shortcuts. Ok for sure mastering Stillwater Dry for Trout helps me with Giant Gourami but I don't see anything less than 10 years of fishing for these buggers to get to the point where I will be saturated and feel it's time to start anew. And that's constantly-on-the-water fishing time of course.
So cracking the code? No way! How many fish would that mean? 50? 100? 1000? 10,000? 30,000? In trout terms I might put it at around 15,000. Of everything I've done, however, Stillwater trout has been the most complex and so perhaps significantly more. I know I learned some pretty serios stuff, at least one of which I would call a "corner piece" (regarding the total dominance of currents on Stillwaters) which came only after well over 25,000...
Gourami: I've had only around 40!! That code is not cracked by a long way but I do have one corner piece and possibly a few edges... and a hell of a lot of blue! I plan to catch more than a thousand, only then will I know anything truly worthwhile about these fishes - for only then might I see the puzzle.
So by "Cracking the Code" I think you mean you're looking for a "Corner Piece"
Right, now I have to crack the immigration code. Hopefully that's a far more simple process than fish!