The texture of the Windows Vista/7 COA below is very papery.
Because of this, the digits of the COA become faded. Hence the product key becomes illegible. This is typically prone for laptops because they have both the COA at the base of the system and because they generate more heat than Desktops. Laptops a few months old can have completely illegible COAs.

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Compare this with some of the original WIndows XP COA stickers (some which are as old as 2001):
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These have a plasticy outside texture and are still completely legible.Â
Aside from aesthetic appeal, the COA is ones right to use Windows, and one may use their product key from the COA with retail media for a clean install of Windows. I have personally can't read my Vista OEMÂ COA, with my WIndows 7 units I put Scotch magic tape ontop of the COA but I shouldn't have to do this.
It is important that the COAs are readible.
Put plasticy or better yet metallic Windows COAs on all new Dell systems.