You are thinking like a human. Software works differently. It's broken down into modules and there would be a module for CTC, CCC, RMD, etc. Each has several lines of query. for example with CTC, there would be a module for each dependent. All that stuff from form 8867 , 15 lines are queried. What you check off as 'yes' or 'no', in the computer sw comes out as 'true' or 'false'. In the cas of CTC and the other modules requiring birthdate, the computer sw has an algorithm. It would be something like this - CD - YrOB > 16. Current year - yr of birth is greater than 16. If this is True, then the credit gets denied. If it is false, then it passes. The point is that all Birth years are compared, not any selected ones. The actual software is likely written a little differently, but thi is the basic gist of what's going on.