Why the different versions on 3 PCs?

I'm a recent user to Norton 2009IS, 3 users. Before Norton I had a 2-year Avira suite licence.

 

Dell desktop 16.5.0.135, IPS not working

 

Acer laptop 16.7.2.10, IPS working

 

Acer laptop 16.7.2.11, IPS working

 

Why are the three PCs on different versions? I have run live update.

 

Is this usual? I find this very disturbing. I checked the Dell last night and no updates had come through for 4 days. I re-installed Norton and ended up still with 16.5.0.135, updates are working now.

 

Can somebody put my mind at rest as I am on the verge of dumping Norton less than a month after buying a 2 year licence.

 

Ian