Added observation: On the ASP video of 4/20/21, Multiple Home Invaders Stopped By Armed Defender, you see a home-carry victim shoot to slide-lock empty and retreat to another room to reload, returning to fire more. Correia's comments are he considers this after the fact, and shifts to his advice to carry as many rounds as you can in your primary carry.John Correia (ActiveSelfProtection) says he has never seen a non-LEO defender need a spare mag in thousands of real life SD videos.
For me, it is more supportive of having your spare mag with you at all times.