is it really that widespread, and is it so even in the high-end prestige bottlings?
I'll attempt to reply to your question as best I can (while realizing my limitations).
Yes, the practice is widespread, but also distinguished by the differentiation between adding allowable caramel coloring for consistency and allowing both boisee and caramel/sugar flavoring.
If it is written into the regs, you can assume that it is widespread...and it is.
Producers can...and most certainly do...opt out of using any additives in cognac...hence the "pale and dry" designations to signify that.
Most cognacs don't stay in new oak barrels for longer than about a year before being transferred to older and less active barrels, because the cognacaise want to limit the amount of aggressiveness and impact of new oak.
The 'high end' cognacs can have the additives, yes. I would suspect that many of them don't; or that at the higher quality end there is less use of additive than at the bottom end/high volume segment...but I have no way whatsoever of gauging that.
I generally think that most of the VS grade stuff is usually rife with additives (and whenever I see a really dark mahogany-red color or deep browns, I assume that 's the additives) but that the really elevated stuff is more likely to be natural and additive-free. But I don't know.
I do know that some of the select, small houses, such as Leopold Gourmel, make a point of saying they do not use additives. But I'd also say the only time you can assume additives aren't used is when it says so on the label or in the accompanying material.
And of course, if a chemical analysis tells us so.
At one time I would have taken this moment to proclaim how precious and pure bourbon whiskey was---but I can't even do that any more, what with the Maker's Mark 46 and such,with the use of toasted oak stave immersion to "flavor" the whiskey. Additives is additves, sez I. The only difference is how you get them into the product.
By the way: I can access the English-language version of ALKO. But I can't figure out yet how to find the sugar listings you guys speak of. Can you tell me how to do that?