I wrote a story once where I named everyone the protagonist came in contact with and gave a mini bio... Because the brain eating alien virus that transplants the consciousness with that of the slug alien overlord, gave everyone a new alien identity. So you had to know the old one first or you wouldn't understand it was a replacement.
It was a lot of typing.
If they ask you about a character being named, just tell them he is desperately important in book six. Absolutely essential.
And since few people extend their trilogies into book six, who knows? He might be.
(If you get to book six you can have him hold the door open so your protagonist can get into the magically guarded building, then see? Absolutely essential.. Good old Trevor.. Always count on him to to the right thing)
Its up to you, really. The rule of thumb is, add stuff to tell the story. Take stuff away that interferes with that.
While its not really telling the story, neither is it interfering. if naming makes it easier to tell the story, then name.
David Eddings had a habit of introducing minor characters completely and then getting back to them in the next series.. A literary reduce reuse recycle effort, i imagine.
But there are a lot of tricks you can play with naming a character. They can be your story macguffin.
I like hiding details behind names, personally. Using a name actually allows for maintaining ambiguity of sexual identity.
So if you are not sure whether your character is a boy or girl or alien sock puppet.. That might be the way to go.
Then you can decide later that since the publisher says you need a strong female character to help sell the novel, Kowalsky the peg legged Magnum 45 pulling partner is now a woman..
Just remember to write the best story you are capable of writing to begin with. The rest is editable.