Hi Jess,
If you'd like to add items to Finds that are no longer in the stores (meaning, you can't just collect them with the YLF bookmarklet), then you can do so by going to Finds - Mine - and clicking on the "Custom Find" button.
There you can add a product name, brand, choose a category for the item (e.g. knitwear, shirts...), add a description and pictures of your items.
I believe items created this way won't show up in searches by other members though.
ETA: every item you collect, whether it's by collecting via the bookmarklet, creating a custom find, or clicking the heart on items other people have collected will end up under "Mine" on your Finds page.
Here's a bit more general info about Finds:
And here are blog posts Angie and Greg wrote about all things Finds:
(This one explains Collections)
I hope this helps?