I have been working on this type of organizing for our Hist. Soc. for several years. We are only 2 or 3 of us working a couple hours a week to sort out items with and without accession numbers (and items with accession numbers in the accession book but not actually on the item), with the goal of entering it all into Past Perfect software. We are mostly a paper archive, with limited artifacts. I had volunteers make a list of what was in each container (drawer/box), adding accession numbers if known. A copy of this list went into the container and another copy into a binder. On the other end, a volunteer typed (how quaint) index cards for each item with an accession number. It has been a very slow process to match up the items to their cards & donors while still keeping our archive open for researchers. (I am not a trained professional archivist, although I have taken some workshops.) We also had a C.A.P.E.S. survey done by a professional who volunteers her time to that group. Her report helped guide us on the conservation/preservation side so that we properly store the items once processed.