For example, when I use Gmail's "All Mail" view, I see that I have 28,537 emails. However, Gmail Backup produced 54,662 .eml files when I did a full backup. I'm not sure why these 2 numbers aren't the same.

These two numbers are not equal because GMail counts conversations, but one conversation can contain many emails (.eml files).

Thanks to //www.gmail-backup.com/count-gmails-all-mail-view-count-full-gmail-....