Allan,
I have some on my Oriental that have been down for over 5 years. I did over coat them with some clear. Please take caution with the amount of retarder that you may use though as I had one set crinkle a bit when I put on a wet coat. Most of the crinkles went away but there were some lines in vinyl as a result. On a Sig Super Chipmunk, I have some that were not clear coated and have been there for 8 years without issue.
Bon chance,
John