Monique Bollen from Gazelle wrote to Martin:

"Our information stops in 1974, we don’t have a building list of the race frames before that date. As the counting starts with 31….. in 1974, it is possible that your frameset was build at the end of the 60s, as we then started building race framesets. (1967-68 to be precise). Your Champion Mondial is really an oldie, one of the first framesets that was built here, we think. It's an A-frame."

From this Martin concludes:

She says that Gazelle started building race frames in 1967 or 1968, so my frame would have to be after this date. On the Gazelle homepage there is a history section mentioning frame number 2000000 being built in 1966, with my frame (2220822) being one or two years after that. I feel fairly confident in concluding that what I have is an A-frame from 1967 or 1968, repainted in the late 70s. I also found a BCM marking on the lugs, meaning Bocama.
On a side note, I also believe that the 2423143 on your site is indeed an A-frame (even if it was possibly built up as a
semi-race bike as claimed). It seems to be almost exactly the same as mine and has the Champion Mondial logo that the semi race bike lacks. The wheel base also seems shorter than on the later semi race frames.