Weight of bulk bags

Hi, I work for a drainage and landscape supplier, when we deliver bulk bags the weight on the ticket says 850kg. It also says for carriage and lifting assume weight of 1000kg.
What weight do I need to allow when working out how much I can put on the lorry?
My manager says the 1000kg weight is for site use and does not apply to me.
Is he correct?
Sorry for the long post.

What do you generally have in the bags?
Any pallet company I have worked for has scales, don’t they have them at your work?
Would you be overloaded if they were 1 ton as opposed to 850kg?