The figures were the ones given by the french editors, compiled by a french mag in 2000 (Backstab) for the french editions.
For the english langage ones, it was estimates given by the main importers.
And it was the sales in France only, even if I'm sure that for the french language editions, it was the total sales made by the editor for all french speaking countries (Jeux Descartes for CoC, Oriflam for all the others).
I also remember an aticle by MOB in an old TotrM where he reviewed the french RQ and explained that the Oriflam sales for France were in the same league as the ones of AH worldwide, but I've never checked that.
Runequestement votre,
Kloster