That's my understanding...in essence, acting like a 'loading a backup' if something were to happen to your collection.
You can try to bulk load from a constructed collection, but it's not easy.
The correct vgc id's need to be mapped to your collection items. If you export an existing vgc collection, you'll be able to see the associated vgc id for each item. Otherwise, you can look at the trailing number in the url address for the vgc item page your're currently viewing.
From what I understand those are the only ways to get the vgc id's needed to build a csv for importing.
Due to these details, I've resided to just adding to my collection little-by-little with my barcode scanner.