What i was wondering was - is there a components league table or similar so that i can guage components against each other? This is an odd question and possibly there is no answer to it but i would appreciate any advice.
As per my previous posts, i am thinking of putting Shimano 600ax components on my bike but i have seen 600ex (perhaps called DuraAce) components for sale. If memory serves me right, these are a higher quality than the 600ax - but i could be mistaken. I am very (VERY) confused by the naming of various sets of components as, to me, the name may be the same but the year is the important bit - a 1983 DuraAce is not the same as a 2012 DuraAce - how should i be able to tell the difference?
I'm not aware of any league table as such, but the Shimano hierarchy has already been stated. Campag has a hierarchy as well: (Super) Record > Chorus > Athena at the top, starting from the late 80s. Lower range names have changed around a bit. As also stated already, don't rule out Suntour. Their gears were arguably the best going in the early 80s, and when you can find them are often cheaper than the corresponding Campag/Shimano.
Regarding your question about the years, the main area where you need to exercise some care is in the gears. Over the years the standard number of rear sprockets has gone from 5 to 10 (and more, but this is retrobike of course...). Indexing started with 6 and 7 speed, and as the number of sprockets went up, so the spacing of the sprockets went down. So you can run into trouble if you try to mix shifters and derailleurs of different years. Some manufacturers used a more or less cryptic code for year of manufacture (see http://www.vintage-trek.com/component_dates.htm
velobase is your friend if you have any specific components in mind.