Listsource partial list help

[Simon Ghandil]

I'm launching my first direct marketing campaign and am using list source to get my list. 

With the criteria I plugged in, I was given about 3,700 houses. I am doing a partial list of 1,000. If I go back next month and do another purchase of 1,000 houses from the same list, is there a chance I will get duplicate houses? 

I would assume that once I purchase this first 1,000 houses, the list will go from 3,700 houses to 2,700. Then next month when I purchase another 1,000 houses, the list will shrink to 1,700 houses. I just do not want duplicates next month when I purchase again.

Also, where it says "Remove duplicate property mailing addresses" is this something I want to check or leave unchecked? Thank you.