As per the website A,Z,W,T,O,R fare buckets are all lower/discounted fares earning 15 or 25 tier credits depending on if saver or smart. Anything other than those on a standard economy fare should be good for 50 tier credits. As far as if its booked into saver or smart I don't think you can tell from the fare code, but if you specify you need luggage included they'll have to book into at least smart I would think. Other than that not sure what else you are asking for.... (from personal experience G fare bucket tickets seem to be at the higher end price wise when economy is oversold or nearly oversold as I've been upgraded to business as a platinum at boarding each time I've had a G fare code, but this is only my personal opinion I don't know for sure).

Edited the above thanks to comments below.