All I have is the old style contender frames. Every barrel that I have works on all of my frames. Some of the barrels were bought as recently as two weeks ago.
There really isn't any such thing as G2 barrels. There are G2 frames and grips, but not barrels. Contender barrels are Contender barrels. The only thing that has changed on the barrels over the years is the locking lugs. Even before the G2 came on the market TC started using a split locking lug on their barrels. On the frames that haven't been converted to the easy open style, the split lugs don't always engage the interlock. So, they don't always have to be changed, but sometimes they do. As I said, it takes less than a minute to do it. Just drive the pin out, remove the lugs and spring, put the spring back in, put the lug in and put the pin back.
Like Contender said, the only thing that is not interchangable from the old-style Contenders to the G2 is the grip.
This is directly from Thompson Centers website:
G2 Contender® Compatibility with Old-Style Contenders
The G2 Contender frame will accept all Contender barrels and their corresponding forends (except Herrett forend). The G2 frame will not accept old-style grips because of the change in grip angle. Blued or stainless barrels are readily interchangeable.
Not that it really need mentioning, but if any barrel will work on a G2 then any barrel will work on an old-style Contender.