Thanks to @spoc84
for hinting at this issue, as I just confirmed it with a test. I had Cano at B2 and Pujols at B1. Took Pujols to B2, so they would start at the same level.
I manually upgraded Pujols from B2-B10. I received the following amount of balls:
When I used the quick upgrade feature to immediately level Cano from B2-B10, I received ONLY the 25 balls from the last upgrade level (B9-B10).
Glu sure is some kind of sneaky!