For some reason I thought when booking a flight your outbound and return flight would have to have the same fare class with the more expensive class being used for both flights. As I'm booking a future flight I see this is not the case.

Specifically, my outbound in 2003 is pricing out as a V class and my return in 2004 is pricing out as T on a single round trip. I'd like to get full credit for my first flight in 2004 and don't even mind paying for it. (I have to use my corporate travel to book this.)

Again I swear that in 2003 I encountered similar situations where all the cheap flights were sold out on one flight and not the other but I was forced to buy V class on both flights. Now for my 2004 flights when I wouldn't mind being forced to buy V class fares I'm able to get a discount on one of the flights.

Is there anything in COs "rules" about this? Has this changed or has it always been like this and I've been imagining things all along?

Completely depends on the fare restrictions. The bottom-of-the-barrel fares often are hard to mix (call a phone res agent, they often can mix and match fares that you can't do manual on co.com). However, I've never had a problem mixing fares of anything V or higher ... and course they're ALWAYS glad to take your money for Y on ANY segment =)

All fare rules specify what other fares they are allowed to combine with, regardless of the fare basis (If a Y fare says it can combine with a T fare, they can combine to form a roundtrip and you get two fare bases, one per fare component). Basically a round-trip fare is two 1/2 RT fares that combine together. Since there is T inventory the CRS computer reads the fare rules and sees that your V and T fares are allowed to combine, and then takes 1/2 the RT fare of each and makes a total RT fare. I'm sure there is V inventory on your return flight in 2004 and they should have no problem combing two V fares for you if you call them.