I disagree. Trek lit writers should not assume they write for the audience that already has the knowledge about the canon background from the TV shows and movies, even if that's the case for the majority of the readers. Any literary work should be able to stand on its own. The story should be understood by a potential reader who hasn't seen the episodes where the characters originated from (in this case, TNG "First Duty") or doesn't remember them anymore, rather than just the people who have re-watched every Trek show several times or regularly visit Memory Alpha and Memory Beta.
I agree with your general point, but I don't think an understanding of this story relied upon knowing Locarno's backstory. It adds an understanding of where his character is coming from, which can add depth to the story. But whether this story stands on its own doesn't depend on a reader's knowledge of the events of "First Duty." Or if somehow it does and I'm failing to recognize it, I still was hoping as I read that this would be an instance where a one-off character was being used without the writer spelling out the events of his life that transpired in the one episode we originally saw him in. More like an Easter egg for those who recognize the character, but not one that diminishes the enjoyment and understanding of the story for those who don't know Locarno was in an ep of TNG.
I don't know. Not that big a deal in my enjoyment of the story - just something I thought as I was reading it.