When using Summon Nature's Ally X or Summon Monster X to summon creatures of a lower level (1d3 creatures of one level lower), does Superior Summoning still provide an extra creature if you roll a 1?
The RAW is unclear, there is no developer commentary on this subject that I can find, and the community opinion seems to be somewhat divided (though somewhat favoring “yes, it basically makes that case 1d3+1”).
Demonstration of community opinion:
Superior Summoning Question—exactly this question. Thread unanimously agrees that you get the extra creature even if you roll a 1. Three for, one asking, two commenting on tangents without addressing the question.
Advice: with Superior Summoning, is it always better to summon one level below your max?—it comes up, one for and one against. Most of the thread does seem to assume it won’t be a problem, though.
Added Summoning (Abyssal Bloodline Power) + [UM] Superior Summoning feat—Combining this effect with others; the question comes up and again scores one for and one against. Also general expression of confusion about this feat.
There are no doubt more; these were just the first hits on Google for this subject. Basically, the feat is a mess (I also came across a great question, which also had no answer, of how it interacts with elemental swarm—clearly, that conjures multiple creatures, but it comes with a variety so which one do you get an extra of?).
Basically, Paizo dropped the ball on this feat, and you’ll have to rely on houserules to determine how it actually works. For what it’s worth, summoning isn’t so strong that this costly feat should come with the risk of it not working a third of the time when you try to use it.