Your last paragraph describes my area. Almost 60% of the sales in my one county, 90% in the other county are FSBOs. Which means I make lots of phone calls to owners, knock on doors, calls to next door neighbors, family members of a seller or buyer, etc, etc. We are very lucky in Arizona to have Affidavits of Value, a document with the sales price stated that is signed by both the buyer and seller filed with the county recorder with each transfer of ownership. I have to pick up those once a week from the courthouse. I always have to track ads in the weekly newspaper, on bullitin boards at the grocery store, watch for FSBO signs nailed trees and in yards, etc and matche them up to the assessor's records and eventually to an Affidavit. I use the Day One/Nova software, it has a program to save comparables from my reports-which do constantly. I have also created a dummy data report and as I pick up Affidavits, FSBO ads, realtor listings I type info into that data report and save to my data base. I now have six years of computerized info on every residential property in my two counties that was ever offered for sale or sold. I keep all documents in my office in assessor's parcel number order--so some numbers have several affidavits because it has sold several times, FSBO ads, realtor ads, photo of a sign nailed to a tree, for the past six years. With this computerized data base I can search for any property that is comparable to my subject, insert it into a report (including a photo) and away I go. Most of my research is completed at the time a home sells or is offered for sale, so when I write up a report I am just tying up loose ends for the comparables I select.
Now to the first paragrpah--I am a little confused. If a property sells, you can use it as a comparable for every subject property you appraise from then on that is very similar. So if your questions is that can you reuse comparables-yes. And you might have comparables previously used from many different former reports but in a different sequence. Just be sure they are arms length transaction as stated in the definition of market value at the top of the Limiting Conditions page. And although the first three comparables should be closed sales, the remaining comparables in a report can be active, pending, expired, withdrawn--whatever will give a picture of the activity for that specific type of property in the market. If there are three homes on the market just like the subject for $50,000---the appraised value of the subject would not be $60,000, no matter what the closed sales indicated!
Sorry about some of the urls not working, I probably made a typing mistake. But access those appraisal boards for that state, do a search for manufactured housing and the right link will pop up.