I've been trained as a landscape designer and have practiced in the trade for several seasons in the past (I'm an occasional landscape consultant now). No one - absolutely no one who is honest, that is - in the US measures the height of a plant specified for a design from the bottom of the pot to the top of the plant.
In my own designs, I always drew the plants in the plan at their "mature" heights and widths. There is no other way to create a "to-scale" design otherwise. In this case, the height is determined by measuring from the ground or root flare to the top of the plant and is always an estimate, as some cultivars grow slightly smaller or taller than others. I always used specific sources for this information.
I sometimes specified optimal planting size by container size or "B&B" (balled and burlapped), but that was in the plant schedule and was subject to the client's budget. The size a shrub is planted at doesn't matter; the size the shrub attains as it matures DOES matter.
If your plan does indeed call for shrubs to be planted at a height of 80cm and the developer is providing plants at 40-60cm, then that developer is incompetent at this part of their job, can't easily source the proper sized plants and is lying to you, and/or is intentionally trying to save money by scamming you.
If this is the case, I'd question the plant in the design - who knows if they're even appropriate to your site? I once moved to a house where a "landscaper" had done a "plant dump" at the end of the planting season, just putting whatever stock he had left wherever he could. He put a shrub that got 15 feet wide 2 feet from the house, and another that got 25 feet wide only 6 feet from the house. He also added a ton of perennials that required excellent drainage to a site that was 100% clay subsoil. He truly ripped off the original homeowners who had hired him.
Make sure your design doesn't have issues like my house did.