1. In a computerized file record maintenance system of the type where, for each individual one of a plurality of record files, a plurality of stored images are successively individually recorded, each said image being so recorded at a date which is spaced by a prechosen time interval from the other images of said plurality of stored images that comprise one said image plurality for a given one of said record files, and each stored image containing all information relating to the status of its file as of the date of its recordation, and each individual one of said record files also having a recorded associated companion historical file containing recorded accounting records pertaining to that individual record file, the improved method of entering a desired retroactive transactional change at its effective date into a prechosen individual one of said record files comprising the successive steps of: a) retrieving from among said stored image plurality for said one record file that one image whose recordation date immediately precedes said effective date of said retroactive transactional change; b) entering all accounting records relevant to said one record file into said one image from the associated companion historical file of said one record file which relevant accounting records occurred during a first time period extending between and including said effective date and said recordation date of said so retrieved one image, thereby to produce a resulting image which represents the status of said one record file as it existed at said effective date; c) retrieving a selected target date, said target date being a date that occurs between and including the present date and up to said effective date; d) backing out from said resulting image using reverse arithmetic signs all relevant transactional changes which previously occurred during a second time period extending between and including said effective date and said target date and which were previously interveningly entered into said associated companion historical file so that all said interveningly entered transactional changes are negated, thereby to produce an intermediate image; e) applying to said intermediate image said desired retroactive transactional change using correct arithmetic signs, thereby to produce an adjusted image; f) reapplying to said adjusted image all said so backed out interveningly entered transactional changes using correct mathematical signs, thereby to produce a corrected image which represents said one file and which fully incorporates said desired retroactive transactional change; and g) recording said corrected image as the working record image.