I think this may sneak a 3kyu. Testing rows for validity is easy, columns a bit more complex, but the 3x3 blocks require some careful management of the data. If not 3kyu, then a solid 4kyu.
This was enjoyable!

Do you want to specify behaviour for strings with length < 5? Or specify that strings have at least 5 digits?

I'm not sure it needs deleting; it's subtly different to the other kata (returning an array of arrays rather than one 1-d array), allowing for either a recursive solution or a small function to return each layer.
Pascal's Triangle is a nice algorithm and this is a cleanly constructed kata.

Thanks for the new explanation...but I have to say it still isn't clear what I need to do in tryCode(), or even if I need to write some function to call tryCode().

By the way, I totally understand the algorithmic and game nature of the kata. It is more that I don't get what you want us to do in tryCode.

I like this one. The addition of the plateau case complicates the algorithm sufficiently to make it 4kyu IMO. Description is clear enough but still requires some thought to figure out the complexities.

I agree with previous comments: the description is not clear enough. A walk through, or description of the first run is needed.

Sure was!