From what I've learned, it used to be thought that these were made by Champion because they were sold in Bicentennial bags marketed by Champion. Later it was discovered that champion obtained many many red/white/blue marbles from Ravenswood and sold them in the Champion bags (must have been old stock because Ravenswood was already long out of business by 1976). Champion also made them but the colors are not as vibrant and the pattern is a little more like what you would expect from Champion. Cullet from these marbles was also found at the Ravenswood factory site, which sealed the deal.
The right marble also has a trait of Ravenswood you can see in all 3 pics (they all show the same side of the marble). Where the red ribbon ends, you can see where the glass stream was cut and it made a tongue that lapped onto the marble. Other makers can show this, but Ravenswood shows it quite a bit.
I'm not sure if these photos are helpful or not. (Assuming I have them in the right spot in my spool box!). The back row I have in with my Champions, and the front in with my Ravens. That said, I'm on the fence on the last two mibs in the front row.