This didn't dawn on me until I experimented with damage+status attacks further.
It seems that if a spell has a status attached to it AND targets every character, it will ALWAYS have a spell multiplier of at least 1
AFTER even after the spell multiplier reduction due to the magic defense multiplier.
It's related to why Dr. Lugae is always able to distribute Poison to all targets (excluding the fact that Poison resistance is not working properly in the SNES versions).
As an aside, you can apply other statuses just fine with this property, particularly Piggy, Toad, and Mini, to continue to set those statuses on the targets, instead of the normal reversion process that usually occurs.
Added new stuff clarifying about how the spell multiplier is involved.
Note: It's different in FF4A Euro/Jap 1.1 version where poison resistance prevent spells like Poison or the Dr. Lugeie's Poison Gas attack to fail altogether.
We have EVEN MORE themes now, but some old ones are gone...