Apologies, Montreal Convention is not per kg, that's Warsaw. Under Montreal art 22 the damages for lost baggage are capped and LX in their Conditions of Carriage art 16.2.2 explain that this is now 1288 SDR per passenger. Thats about $1700 equivalent.

I would imagine LX are a bit more lenient when it comes to not having receipts for F class passengers but there is only one way to find out, unfortunately.