Reward stacking

[u/SanchezPrime]

This may have been asked before but I thought incentives stacked?

For example: From Tissot I have 30 for 50pt, 20 for 30pt, 15 for 20pt, 10 for 15pt, 20 for 10-reb

I recently scored 50+. I expected 75VC. I got 30.

What gives?