Shimano has new models of their groupsets every year but the lines generally keep the same names. This makes it difficult to figure out what year/version a particular bike has. Is there an easy way to figure this out and also determine which components/groupsets are better than others?

For instance, if I have Tiagras from 2009 would they be better than Sora from 2010?

Shimano has new models of their groupsets every year but the lines generally keep the same names. This makes it difficult to figure out what year/version a particular bike has. Is there an easy way to figure this out and also determine which components/groupsets are better than others?

For instance, if I have Tiagra derailleurs from 2009 would they be better than Sora derailleurs from 2010 for a road bike?