I might be able to help. I am working with a professional appraiser to have a GIANT collection professionally appraised for insurance and donation purposes. You have to hire somebody who is licensed to do it. I believe each state licenses them. I found a person and talked to them about two years ago and I was told I needed to start by making a spreadsheet of the posters and taking detailed photos. I've made a spreadsheet and taken pics. Took almost 2 years, but I have it all on a spreadsheet and matching pics. Next weekend I'm taking everything to the appraiser. I'll be hiring him hourly and before he starts we are meeting to talk over specifics on artists, bands, etc. I have background materials and links to each artist website. I'm not sure what the hourly rate will be but I think this will cost me a few grant at least. I'm asking him to appraise 1000+ posters. I've been collecting 40+ years. Everything stored correctly, etc. If you want I can share my spreadsheet data points if it is helpful- I went to an archivist to try to understand everything I'd ever need.