Do you know if these are meant to be owner's marks or manufacturer's marks?
The reason is that the coronet/crown designs or representations seem somewhat dubious.
The first and third, with its three strawberry leaves, appears to be a bastardisation of a British Marquess coronet
[image1] (ignoring the cap), except that it has two "pearls" rather than one between each strawberry leaf (the small balls on the uprights are called "pearls", although they are not). Many European and Asiatic coronets and crown bases share a similar pattern of
fleur de lys-pearl-fleur de lys but I'm not aware of any coronet or crown base that has a
fleur de lys-pearl-pearl-fleur de lys design.
The second and fourth resembles a British Earl's coronet
[image 2] (minus the cap) but with one strawberry leaf less. This coronet forms the base of a faux Austrian
[image 3] or Russian
[image 4] Imperial Crown.
The Princely hats and crowns of the Germanic (Holy Roman Empire) states and families
[images 5 & 6] bear very little resemblance to either of the coronet/crowns posted above.
Wikipedia has an excellent page on
Heraldic Crowns but once again there is really nothing that comes close to resembling either. I'd suggest that even in the 1690s, any princely or aristocratic owner of the furniture would have a pretty good idea of the correct representation of their personal heraldic device but, to me, these two just seem to have little basis in reality.
Apart from that aspect, the central monograms or cyphers may well be genuine and accurate representations but I'm sorry I can't help in that area.
1. Coronet of British Marquess (regulated 1661 by Charles II)
2. Coronet of British Earl (ditto)
3. Imperial Crown of Austria (made 1602 for Rudolf II)
4. Imperial Crown of Russia (made 1762 for Catherine the Great)
5. Holy Roman Empire Princely Hat
6. Holy Roman Empire Princely Crown