Huh... just realized.
When you fight someone, you can see their Defense score in the URL for the page, even though it doesn't show you in the page. Look for defense_point in the URL, and skip past the %3D. It also says enemy total cost? The total cost it's showing in the URL is more than the DEF cost on the page, though suspiciously, the last two two-digit numbers of enemy_id correspond to this number and the DEF cost that the page is showing me (in my example, it's <number><total_def_cost><displayed_def_cost>). I think this is coincidence, but eh.