I had to attach this separate sheet of paper with our old address (we moved last year). The instructions just say to put your name(s) -- I put both of ours because it is a joint petition -- and the immigrant spouse's A# at the top of the sheet, and then the number of the item (Part 3, no. 9). This item only requests the old address(es) and the dates you lived there.
Note the instruction about "initial evidence" pertains only to the criminal history question, and the "detailed explanation" goes toward the other yes/no questions, which by their nature require explanation. The specific, italicized instruction in parentheses following the question about residing at any other address only states that one should attach a sheet with all addresses and dates. It doesn't say anything about putting a reason for moving.
James got a reaction from Family in What to do now that family reunification program extended to Colombia et al. for those with pending family-based petitions?
James got a reaction from VeeNDee in "Change of Address" question on I-751