InfoPath Dev

Clay, Can you show me a simple coding (or guideline) on how to check the missing field and create the field in old form's xml? Because I'm quitea new bird in using infopath, so hope that you able to give me some advice for this infopath. Thanks a lot!

Now I can confirmed that the drop down in the old form does not bound to the new field. So, is it any way to make it bound to the new field?

I had requested to modify 3 template, let say template A, B and C. I added a drop down list control for each of the template and publish to the sharepoint but there is one problem happen regarding to the old form in sharepoint. Since template A is no problem, I don't know why when I open the old form by using template B and C then ...