Hello, woodpeck. Thanks for your message.
My source is IGN indeed, but you can find some differences in many points (almost always just 1 meter), depending on zoom level. For example, a peak may be 982 with some zoom level, but 981 with another. I don't know which one is more accurate, I don't know if the difference comes from a second measurement over the years... I simple chose one. In fact, when I go outside with my own GPS, I usually find even greater differences. The height of peaks depend on the sea level, and the method used, so I simply trust IGN. So... it's just a matter of giving a "very close height". From the hiker point of view, height information is just useful information, relative to their surroundings, in my opinion. Height information from IGN is a very useful information for hikers, and I've tried to "migrate" that information to OSM. If community is against this, I'm fine with the deletion of all my editions.