I won't worry too much as long as you don't consistently heat the tyres up with excessive speed. I had one of mine "plugged" a month ago as well and its been fine, despite recording 153mph on a recent trip up north!
The reality is, any tyre could have been plugged before being acquired by its new owner (assuming it was bought as a used vehicle) and yet, we pay no attention to the risk. However, once the puncture which results in a plug occurs while the vehicle is in our possession, we develop some kid of phobia to explosion at high speed - what you don't know.....
Migration info. Legacy thread was 6280