General
Armor as seen in the gladiators dossier is the sum of all your armor-pieces + 2 x DEF you don't need to know that figure because it is useless.
Much more interesting are the armor values of your individual pieces (because a strong leg piece won't help you when getting hit over the head).
The armor value doubles in game but - unlike your health points - can not be regenerated.
Strategy
You might want to bolster your weakest and must crucial parts (no jockstraps avaliable ;). For dual wielders: legs. For glads relying on their shield: shield arm. For protectors a solid breastplate might be usefull too.
But you might as well decide to go for items like lorica-segmentata or chains-mail because you need their base bonus properties. The latests have crap armor but other pros.
Anyhow your gladiator level of health points and the other bonus stat of your gear are more important than their armor stat.