Defenses are specifically defined as sandcasters, repulsor beams, and beam weapons used as missile defense, or nuclear dampers, meson screens, and configuration.
Can you state where is this specifically defined?
As Mike says, Armor is in the defenses block of the USP, and I guess everyone will agree armor is a kind of defense (what else is it, if not?)
OTOH, as Rupert also states, as the same wording is used (penetrating defenses), assuming armor must also be penetrated would also mean the spinals would only roll more times if the first one does damage, and I guess we’ll agree this is not the case…
Using logic, I understand the several rolls from a Spinal should be applied nonetheless, as the sheer power they throw is this way represented (in MT, where higher TLs are also in the tables, some bays may have factor over A, but they don’t roll extra rolls, as this is only for Spinals). And any such rolls overcoming the armor would suffice to trigger the various critical rolls
OTOH, I agree with Mike is difficult to understand how a ship may be affected by a critical if armor is not overcame. How can you destroy the bridge without penetrating the armor?
I see it as a case of poor wording, and I frankly think it can be interpreted both ways