I categorize my photos by content, and assign a unique number to each that reflects the content of the folder they reside in (File for flowers potted, wild or garden grown would get an assigned identifier of FLW101, WFL101....), or for birds (Seagulls - SGULL101, SGULL102...). I use a spreadsheet with spate tabs (worksheets) for each category. Then within that worksheet, I list the name of the file down the left side. I list the Agencies across the top. In each cell of the spreadsheet I change the fill to either green or red; for accepted or rejected form that particular agency. Once an image sells, I change the fill to blue, and place a number count in that cell.
I can see at a glance which agency sold which photo, and how many times. I also track the sale $ on the first page of my spreadsheet by: $ pending pay-out threshold: $ total paid- out: and then I also keep records of number of overall opportunities for sale, cumulative of all agencies accepted files available.
It is very tedious and organized, but I run this as a business. I know where to best spend my energy.
Hope this all helps,
Good Luck,
Rick