The spec lists properties for an abstract "Bluetooth device" here but does not include a property for storing manufacturer data. Manufacturer data is referenced in the non-normative note explaining how requestDevice matches devices against filters (just below the Bluetooth interface definition):
To match a filter, the device has to: [...] advertise manufacturer specific data matching all of the values in manufacturerData if that member is present
To address this, the spec should add a manufacturer data property to the list of Bluetooth device properties and define steps for replacing the manufacturer data when new advertisements are received.
The spec lists properties for an abstract "Bluetooth device" here but does not include a property for storing manufacturer data. Manufacturer data is referenced in the non-normative note explaining how requestDevice matches devices against filters (just below the Bluetooth interface definition):
To address this, the spec should add a manufacturer data property to the list of Bluetooth device properties and define steps for replacing the manufacturer data when new advertisements are received.