Properly made, methode traditional, fermentation rather than carbonation is indeed done with a crown cap and a system of gradually moving the bottles on v shaped frames so that the sediment deposits at the cap end (remuage) . They then are passed upside down into a refridgerent bath until the gunk freezes and it’s pulled out with the beer top.
The liquor d’ive forgotten is then added to make up the volume. Champagne brut is really dry, and don’t forget that champagne is at the northern end of viable commercial winemaking in France (see climate change) so chaptelisation would have been earlier. Sugar is added to make it demi sec or sec really. Not because of the harvests at that stage.
