Collecting CoA stickers is actually pretty difficult, especially on laptops. From Windows 95 to somewhere in the middle of the XP lifecycle, Microsoft used those rectangular stickers with the ink embedded in the paper and sometimes with a plastic film over them. These stickers hold up best over time but they're a royal pain to remove because the adhesive starts to compromise the integrity of the paper. If you accidentally rip into the paper from the bottom, you easily start destroying the key letters.
But bad adhesive is really the only issue on desktops. On laptops you have to deal with wear since the sticker is on the bottom of the unit. It's an all too common problem for the plastic to break and gloss to wear through and eventually destroy the key making recovery impossible. It gets worse though because on newer CoA keys from mid Windows XP and beyond, Microsoft went to cheap paper with the keys printed on with like a laser printer or something. These stickers wear very easily and won't last a year on a laptop if you don't like cellotape over it to protect it.
