Hello Alison,
The kerbweight is a rather meaningless figure, as the actual kerbweight will vary depending on what extras have been fitted. even the type of paint has an impact on the weight of the car, so it is unlikely that any published figure will accurately represent your particular car.
It has little significance when it comes down to towing. You need to be aware of maximum weights for both the car and the caravan.
The kerbweight is only of significance if you have re restricted driving license (Class B only).
If you are concerned about the 85% recommendation, please remember it is only a guideline. For novice towers always try to keep the weight of the caravan as low as possible.
If you wish to pursue the kerbweight, then please only use information from your handbook, or the dealer or manufacturer. Information from other sources may not be accurate.