My local gaming group is at a disagreement with the way the rules are written. At present, the rule we're quibbling about it this:

"....a player may purchase new units for his force (or replace lost units. Players may only use AP from their AP reserve to purchase additional units. Players may choose to save unused AP for use in later Campaign rounds."

To some, this says "Players may only spend AP on units." To others, it's, as written, saying you can't use AP from other sources (re: teammates) to purchase units. The other argument given to support this is that it specifically forbids you, in the rules, from buying UNIT upgrades at all, and differentiates that heroes further cannot gain unit upgrades (save for hades vet) and can't purchase upgrades. It also doesn't forbid you from purchasing platoon upgrades in the beginning of the campaign when initial lists are built, but it does forbid, as mentioned above, buying unit upgrades.

In some instances, the rules are very specific in what they allow and disallow, and in others, it's confusing and up to interpretation. The FAQ does not answer the question.

What I need clarified: Can you buy PLATOON UPGRADES during a Hades campaign, or only at the very start?