Hey again Fantam_Mayfly!
So when I say “Backup” I mean taking the entire project folder, in Windows, and copying it somewhere else as a theoretical “Save Point”. Exporting things doesn’t take the project, it just takes things out of the project to be imported again somewhere else (or back to the same project.
Honestly .fbx is typically just for models and such. Maybe it’s not as great of an idea for this. If you do regular backups of your project you can easily migrate things from a backup to your current project. That’s simply a “Migrate> All dependencies> Select root folder for project you want to migrate to.” Granted, that would still require fixing references and such if you want to keep bloat down and not have multiples of the same texture.
Most things can be used by multiple other things. Such as Materials, etc. Those maps can have as many things like that as they need to. You don’t need 51 door BPs for 51 doors, you just need a single door BP referenced 51 times to create/destroy doors as needed. You see what I’m saying?
And don’t second guess yourself there, you had it right. Build data is for things like baking lighting and static meshes and such for the outgoing build, not assets mid-production.