I've noticed that several of the accepted solutions work only for max two passes. They are accepted because all unit tests for the solution have cases that indeed require only 2 passes. However, it is possible that calculating the result may require three passes (e.g. for Sep 29 1999). I think such case should be added to the test suite for this kata, to catch invalid, hardcoded solutions.

This solution is invalid - it assumes there are at max two steps.
In the case of Sep 29 1999 there will be 3 steps:
1.) 9 + 2 + 9 + 1 + 9 + 9 + 9 = 48
2.) 4 + 8 = 12
3.) 1 + 2 = 3
Maybe such edge case should be added to this kata unit tests?