Hi,
NCH programs have a 6-month free update period from the date of purchase. It means that any version released up until the 6-month period will be applicable to the license that you purchased. Beyond that period, the license will not work and you'll need to purchase another license for the newer versions.
You can always go back to the previous version that applies to the purchased license for free. You can look for the older versions from the link below.
http://oldversiondownload.com/
I hope that helps.