They could be but not necessarily.

Different powders will burn at different rates depending upon pressures which may not be linear. There may be linear portions of the pressure / velocity curve and you may find that various powder manufacturers will tend to publish data on a flat portion of the curve. generally when you get above the top listed load is when things can get hairy with the pressure / velocity curves.

When you chronograph your loads and work up in say .2 or .3 grain increments you may reasonably expect to see equal velocity gains with each change in powder charge. There will be a point where you will see a lower velocity change with the powder charge. This is where the pressure is going to start spiking and go non-linear. AKA - time to back off and back down.

Some powders such as WW 296 or H110 warn against going lower than the listed minimum due to possible pressure excursions.

My advice would be to check several sources, different bullet manufacturer's data as well as the powder manufacturer's data to come up with a range of loads.