If you also include lots of other things like standard layers, text styles, dimension styles, table styles, and maybe a few other frequently used blocks, it'll be inconvenient to say the least to have to update them in separate drawings when you make changes.  By having all this stuff in one template file you only have one place to go and then resave as a DWT when you're done.

 

So when you have the ANSI A layout title block all working add a new layout and do the same setup for an ANSI B.  All the other things in the file will come along for the ride when you open a new drawing with this template.  And if the unused title block bothers you in a new drawing, simply delete the one you don't need.

 

Dave.