It would be nice if there was a warning that pops up when "Load your collection from a file" like "This will remove current collection and replace it with the cards from file." I forgot that and had my collection wiped but good thing that I had a local backup that I like to do after adding tons of cards.
To see this working, head to your live site.
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There is a merge button for the kind of scenario you were looking for:)
I know that but clicked on "Load your collection from a file" by accident.
I’ll add a warning
Thank you, this would save many collections from mistakenly clicking on "Load your collection from a file."