I collect beer caps of brands from the Netherlands also on factory signs and inside pictures. I have in my collection also some the inside sets and sets from non beer products.
Old Dutch cork-lined beer cap: Brouwerij De Witte Leeuw Sluis (red/white)
Negative preserver sheets, first I sorts them by some categories (Dutch, Belgium, only pictures, only one letter, the rest) and than I put them in on first received first stored basis. I put them also in a database. My dutch caps are on the whole of my hobby room on circles from carpet.