I am sorry if I am being pedantic but I do not see anything limiting the addition of a second AA gun.
a. Gun 1 and 2 are AA guns.
b. Gun 1 and 2 roll one die for each opposing aircraft
c. Gun 1 and 2 roll a maximum of 3 dices
Those conditions are all true from my example and match each condition in the rule. Clause b should be modified to include"roll one die for each opposing aircraft not yet targeted by an AA gun". I agree with you how AA guns should be played but I guess my inner rules-lawyer rebels at the absence of the governing rule for AA gun interaction from what is printed on the page.
BTW I would take a moment to thank you for your work on this hobby and you-tube channel. I have enjoyed a lot of the content you have produced.