Otherworldly Steed Hit Point maximum?

Question

The level 2 paladin spell find steed summons an otherwordly steed, with these stats:

Con 14 (+2 mod) [...]
HP 5 + 10 per spell level (the steed has a number of Hit Dice [d10s] equal to the spell's level [...]
Using a Higher-Level Spell Slot. Use the spell slot's level for the spell's level in the stat block.

So, if you cast the spell at second spell level, the steed is a creature with two d10 HD + 2 times 4 hp from Con bonus (+2 per level or hit die of the creature). That means, the maximum attainable hp for this creature should be 24 hp. However, the spell also tells you explicitly that the creature has 25 hp (5 + 10 x 2) initally.

How is that supposed to work when you heal the steed? What is the hit point maxium of the Otherworldly Steed? Can you heal it back up to 25, or only to 24?

Likewise, at higher levels: say you cast the spell at level 9, then the steed would arrive with 95 hit points; but the hit point maximum of 9d10+9x2 from Con would be 108. Can you only heal it back up to 95 points, or to 108 points?

Answer 1

Starting & Maximum Hit Points Equal 5 + 10*Spell Level

When you first cast the spell upon learning 2nd level spells, the steed is summoned with 25 hit points (base of 5, plus an additional 10 per spell level for the spell).

Remember that the steed is not a player character and is not subject to the same rules for hit points that players are. At best, it should be considered a monster and the book is specifically telling you how to scale its hit point growth.

The primary purpose of spelling out its Constitution modifier as well as number of hit die is that the steed will be around long enough to benefit from resting and thus there's a need to define those elements.

---

Notably, this kind of language regarding hit dice is missing from other spells which summon an ally like Summon Fey, Giant Insect, Summon Aberration/Construct/Elemental, etc. Those spells do follow the base formula, however, they all have durations which are short and most likely preclude any kind of healing that would come from a Short Rest. However, there is an edge case where someone tries to heal them using the Healer Feat:

That creature can expend one of its Hit Point Dice, and you then roll that die.

Even still, this being an edge case is likely to be readily resolved by virtue of the creature lacking any stated hit die in their stat block and thus ineligible to benefit from the feat.