Used Time Machine to set up new mac now what

HI, I had a 2007 mac pro. Downgraded to a 2012 mac mini. I am not on the computer much anymore since the advent of the iphone and the mini is all I need. The mac pro was backed up to the time capsule for several years before I got rid of it. I set up the mac mini using the time capsule backup of the mac pro. My mac mini is now, seemingly, exactly how my pro was. It runs flawlessly and I have used the relatively few pieces of software I have without issue. My concern now is this; why should I have to delete the entire time capsule backup to start backing up the mini? Why can't it just pick up where it left off? I can't seem to find anything in my searches to help me along on this. I was hoping it would just back up to the existing backup. I am sure my thinking is flawed somehow.....any suggestions on how I should approach this? Thanks, john