Assets are listed here: https://itch.io/game-assets/on-sale/tag-pixel-art - there are 2900+ assets for pixel art on sale. You'd have to scroll through all of them to check if your assets are there.
If I search on "Untied" I see your assets and that they are on sale. So I don't think there's necessarily a problem with visibility, probably just that you're browsing the games' sales section, not the assets section.
That's true- Most of the other assets on sale also do not show up on the Sales and Bundles pages, although I guess I thought they would. The pages do show a mix of assets and games. I wonder if those particular pages are curated somehow?
I have encountered this issue with sales which is still present, but I'm unsure if it has any bearing on this.
Incidentally, after restarting the sales today I got a couple bundle purchases, so perhaps something did refresh somewhere?
