I don't want to get into the specifics but I found it to be a bit too much. Not enough to bring down my enjoyment of the story but enough to make me say "not again" when new characters show up. I know some people enjoy seeing characters from later Treks showing up but, to me, it's a bit too coincidental some of the people that show up as either one shots or continuing characters. I'm not about to go through each of the books again and list them here. That being said, Vanguard is my current favorite series closely followed by Titan. I may not continue with Titan depending on if it gets back to it's deep space exploration or keeps hanging out on the fringes of Federation space. Hopefully once the Typhon Pact story is done they'll be back "where no one has gone before."