Consider using AutoText fields rather than IncludeText fields. I admit that my use of IncludeText fields has been limited. I know that AutoText can include legacy form fields (as well as content controls). Automated Boilerplate Using Microsoft Word
Unless you have a need of them, I would recommend using Content Controls instead of legacy form fields (but not with them).

I assume you are not using the Master Documents "Feature." If you are, read the linked article.