I dont know where you heard that from.
3m and all the other manufacturers gaurantee the material for years.
I havnt had any problems when Ive done the graphics designs for other people and I do like to experiment a bit with the unusual vinyls.
Always interested to hear about problems just so the problem isnt made again......
For reference.....Ive used sparkle-brite vinyl for the silver, metallics and solid colours for the outlines and these all come with a 5 year gaurantee..........Ive had them on the boat for 2 years so far!:-))