Themed Packs purchased through Ko-Fi offer artists advanced access on many conceptually similar images at once.
Paid Stock Packs are affordably priced packs that are rotated regularly to bring new variety to your resource collection. Old packs are retired then moved into submission rotation in the DeviantArt gallery. Purchasing a paid pack gives you access to all the images at once, years before they will be released publicly.
Premium Packs are more permanent themed packs which feature special content available only through Ko-Fi.