You buy the program and you do own the program forever. What you don't own is perpetual update service. To maintain your automatic update subscription, you have to pay when the subscription expires, just like any other renewable service subscription, or magazine or newspaper subscription. Some antivirus programs don't offer any sort of indicator at the end of the paid subscription period - they just quit updatin'.
Now, I dunno for sure if this has anything to do with what Phoenix experienced, but Symantec/Norton antivirus .dat files typically are updated on Wednesdays. There are occasional exceptions to that, for instance in the event of the breakout of a serious new threat, or a major change/patch/update to the application or scannin' engine itself, but generally, its weekly. NAV isn't alone in this - lotsa others have weekly-only regular updates as well. One thing about Norton is that the manual update method will get you the latest files as of the release of the manual update file you download, and there can be one or more every day of the week. As mentioned, the manual update can be used to update currently supported, but subscription-expired, copies of NAV, too. Thats not unique, but its not all that common, either.
I frequently get asked by someone who's computer I just disinfected, "But how could I have gotten that virus? I have
xxxx antivirus, which came with my computer, it loads at boot, and I run regular scans with it!" They're generally astounded when I point out their update subscription expired a couple years ago. Even worse - and not infrequent - is discoverin' an older, long-expired antivirus program that never had been registered or updated. Ownin' a raincoat ain't quite enough ... ya gotta put it on, and, if ya want the full protection it offers, ya gotta make sure ya button it up and that it has no rips, tears, or split seams.
I'm also a bit perplexed by Phoenix' sayin' the new subscription dates from purchase - in my experience, generally I've found a subscription renewal resets the clock effective with the original anniversary date. Can't say why that might've been experienced; I just checked my NAV, and indeed its subscription expires a year from its original anniversary date, though the renewal was purchased about 6 weeks prior to the expiration.
And just for grins, I'll mention, though not say how, that a
full uninstall/reinstall of many, even most, time-based-subscription dependent programs will reset the clock from the date of reinstall so long as the application in question still is supported by the vendor. A simple Add/Remove Programs uninstall won't do it, but there's a way.