What do these numbers mean (Duplicates)?

[Sloppy Jalopy]

If you go onto the album and sort by Duplicates, the numbers range from things like x1 (2) to x11 (12). What exactly do these numbers mean? I am afraid to sell the expensive ones in this album that are x1 (2) in case there is a difference, but I can't seem to find a difference.

[ƙυεĸɪ⓮]

number inside the brackets = the amount you have overall
number in front of the brackets = the amount of duplicates you have
so if you sort by duplicates you can empty the album and still keep one card each

[TheBlindGaymer]

I have been wondering the same thing. So glad to finally have an explanation. Thank you so much.