From the special rules of the Storyline I for October:
"* Any unit with a defense value, modified or unmodified, of greater than 23 has a defense value of 23. "


By a strict, letter-of-the-law interpretation, if one was targeting a unit with a base 23-defense this would nullify the pilot defense modifier, evade modifier, assault order modified, capture modifier, called shot modifier, friendly fire modifier, indirect fire modifier, DFA modifier, charge-around-blocking modifier, hindering terrain modifier, camoflague, etc?

Am I missing something, or is this correct?

Determine the defense of the unit with modifiers (just like you listed), if it is greater than 23, it becomes 23.

So if your base defense is 23 before modifiers it will be no greater than 23 (it could be less if modifiers are negative)

see it as corrosive atmosphere PC, maximum defense (for any action) is 23 .

so when taking a indirect ranged assault from hindering terrain on seka pride with aiko you would only need a 23 to hit.