I was following until the very end where you hoped the monitors would take the new field as well as the original smaller ones. You're saying you want duplicates or.......?

If you want to permanently merge those 4 fields together, this is the easiest way. I'd rename the 1st field to the 200 example, then merge the other 3 into it. 

http://www.youtube.com/watch?v=l_fgpbqJ-yw

Takes 2 fields you choose and merges all the info into one. It will not magically re-make one new boundary for that field. You'd still have the original smaller boundary datasets. If you needed one new big boundary, I'd wait until you had them all merged and then freeze or trace boundary on the best data you have for that field and it'll make one for you.