That's what I figured. It's just a theory, but I think if you went up to 62% (a la Craig), at 40 seconds, you might start getting a gum line.
Let me put forward another guess. Gentle stretch, right? No slap technique, correct?
I've been thinking about the gum lines associated with ultra fast bakes and I guess, for me, the key is to keep the pizza cooking on the floor as long as you can without burning while having a really large fire on top so you can get the crust and the toppings to cook immediately. Lifting it to get top heat during the 1st stages of baking maybe detrimental and may contribute to gum lines because the bottom gets deprived of a direct contact with a heat source from the floor.
I noticed with my recent bakes that I don't lift the pie anymore unless it's almost done which is right around 40 secs. I turn it maybe 3 times, sometimes I don't even lift anymore unless I am looking for more color on top but, in my experience, the spotting around the crust will come out during the 1st 15-20 secs. I could literally see the blistering within 5-10 secs after launch. If it doesn't come out by then (within 15-20 secs), it's not going to be as pronounced as I would like it to be, in my own experience (some may have a different experience, maybe depending on the oven and dough). When I get the spots but they are not pronounced or blistered, for me, that means I didn't get enough top heat during the critical moments of the bake (which is the 1st 20 secs).