To take that a little further, there is hardly any design changes. At one time the product line was more definable. Most of the model 12's currently lean towards longer range accuracy. Often including a better or higher quality of stock. That would include some laminates. specialty stocks for varmint and competion. Actions include some forms of the PTA but not all. The forum provides some of the history through Savage corporate catalogs. Here is the link to view them. The format is not perfect but at least there is valuable research data there.

http://www.savageshooters.com/content.php?275-catalogs