1964-1969 28 gauge sales in N. America 1678 guns, Table p. 253
Grade 1 613, special order 71, Pigeon 141, 21 special order, Pointer 21, special order 5, Diana 82, 16 special order, Midas 38, 13 special order.
Pie chart p. 339 28 gauge sales 1964 -1977 - 1556 hunting model, 1162 Skeet. In the same time period Gr. 1 hunting - 477 were 28 inch barrels, 541 were 26 1/2 inch.
Yes, I know the total doesn't agree.
Despite there being a significant number of 28 gauge guns in N. America, they are mighty thin on the ground in Canada. I have never seen a 28 gauge Superposed in W. Canada. I have seen lots of 20 gauge including quite a few nice graded guns, just not 28 gauge.
This will be almost all the Browning guns of this period, I would think. FN retained world rights to market the Superposed outside of N. America.
If anyone ever tells you that Browning/FN never did that, immediately view them with suspicion. New variations to common understanding are discovered all the time.