I started noticing this in my hack...
The determination that a physical status attack is applied onto a character/monster is if the existing status is applied already...
If the "weakest" status in a multi-status physical attack is not active, it is applied along with the other statuses, even when they already active.
For instance, a monster that can inflict Poison+Curse attacks a target that already has Poison status.. Curse status can be reapplied to said target.
If the same monster attacks a target that has Curse status, Poison status can't be reapplied.
To properly put this in perspective, I wrote in a different post that I was able to apply Darkness status (via a weapon) and then apply Charm status (with the Charm Harp) afterwards, despite Charm status having a lower priority than Darkness. So, it's actually very easy to reapply weaker statuses such as Charm, Sleep, or Paralyze with physical attacks to monsters that already have Piggy, Toad, or Mini status already applied to them...