Thank you for your answer!
In a German-language article I found the following information, which speaks of a higher tuning of old bassoons. I translated the passage into English.
"In 1858, the French government set up a commission which, the following year, already fixed a binding tuning of a' = 435 Hz for France and which was joined by large parts of Europe within a few years. Investigations of surviving tuning forks and of historical wind instruments show, however, that the introduction of the standard tuning was only tentative: numerous early bassoons by Wilhelm Heckel (after 1877) still stand at around 446 Hz or even at 451 Hz, the English "Old Philharmonic Pitch". This proves that in some places the standard tuning was not introduced at all or was abandoned after a short time."
However, this is about the 19th century, not the 18th century.
But when you listen to an 18th century bassoon and compare it to the sound of a modern bassoon, you notice how different the tone sounds. It's a little rougher, more gnarled, I think. Some time ago I read something about a rubber mute(?) which is found in modern bassoons but not in the old bassoons, and which is supposed to make modern instruments sound "softer".