[scarby2]

they often only attach one barcode to the bag. (the one around the handle)

These can get caught on things and detach occasionally. It's rare enough that it will probably never happen to you in your lifetime but common enough that it happens to many people every day.

given that over 13 million trips were taken on air canada alone even if they lost 1 in every 1000 bags (assuming roughly 1 bag per passenger which may not be accurate) then there would be 13,000 bags lost every year

[wh0knows]

They usually attach a barcode wrapped around a handle AND a sticker placed somewhere else as a backup. The warehouse had thousands of bags, it would be an unprecedented number of bags to have both lost their bag tags, the backup sticker, AND did not have an additional personal tag attached.