Lost All Of My Picks In Lightroom

Q: I picked over 200 photos, copied them to my main collection and now when I filter for the picked photo, I get nothing.

A: Yes, that's right! Somebody at Adobe in San Jose decided that flags, both: Pick and Rejected are local to the current collection. This means that when you copy or move a photo from one collection to another collection, the flag is not copied along.

Since you copied the photos from your main collection:

1. Go back to the main collection
2. Filter for the Picked photos
3. Either assign a star rating or a colour or even a keyword. It's usually not a good idea to use keywords for temporary info. They are global settings and will keep across collections. They will even carry across to Adobe Photoshop Bridge and most other softwares if you have set the Automatically write changes into XMP, see: Lightroom — I Can't See My Keywords In Bridge for how to do it.