Heavy Box Labels on Master Cartons?

I have 4 cartons (shipping between 100-150 units of each size). Supplier said 2 are 14kg and 2 are 20kg. I believe I need heavy box labels on 4 sides above 15kgs. My question is, should I just put them on all cartons in case the 14kg one gets flagged? Is there any consequence to marking it as heavy if it’s 1KG under the minimum? Thank you!