Which Tray Files?

What I have done is to place a Tray into my game. Then I will open up My Library to see what lots are in that tray. Once you find what you wish to keep, you can place them in a brand new game save. It's tedious, especially if you have many lots, but once you have what you want placed into a game save, then you can delete everything else in your Tray. Upload the lots you wish to keep and then they'll be in your Tray. Voila. All done and all set.

I had saved 7 Trays on my desktop and decided I had to sort them all out. I was able to recover everything I wanted and now they are all in 1 Tray. I just need to go back and delete old game saves, now. I just wish Sims4 used a similar system as it was in Sims3, where the files were named as you gave them a name in the game. It would be so much simpler.

Hope this helps.

I don't understand what you mean by new game? This is all a fresh install of Origin and packs no saved files of any type in Documents. Can't I just copy and paste particular files from an old Tray folder into the current Tray file for my own vacant lots I built a few years ago? If I knew which files those were, it won't take but a minute. Household Binary? BPI file? HHI File? Room File? BluePrint file? TrayItem file? I just want the file for a vacant lot/my own builds.
ETA: there are 779 files in my old tray folder. I don't want to put the whole thing into a new TS4 folder.

@rosemow, do you know which of these files listed pertain to my own vacant houses or community lots I built?

ETA: But thank you @GalacticGal , if I don't get an answer which of these are empty lots/builds I will try it the hard way and delete from inside the game. :/

I use Sims tray importer, it lets me make zip files of lots or households I want to save. I keep them in an external HD, and just unzip them as needed and stick them in my tray files.