[Glencook-fans] Rereading Instrumentalities of the Night

I bought these in hardcover when they came out. Hey, new Cook gets bought, sight unseen. I remember liking them but not being that impressed. With pandemic downtime, I've given them a reread. I have to say, they've grown on me. There's a lot going on here, and a lot I missed that first time through. Does anybody remember if Glen said anything about a fifth book?