The first blast or so, everything is going to be hard to tell if you are making progress. But that's not really an issue as the novelty of doing the program a new should be enough to stimulate muscle growth, and of course you are pushing yourself hard. So no sweat there.
One you've been through a blast or two, gotten a good pool of MRs and a solid loading set lifts. It works like any other program. You compare what you did before to what you did the last time you did the lift. If you squatted 300x10 3 weeks before, you should hopefully hit 300x12 or if you're feeling good that day, throw 310 on the bar and try and match. (or whatever, I'm just using some abtirary numbers / rep scheme)
Same with the muscle rounds. I personally like to have a big pool of MRs, so some I will only hit once every 4 to 6 weeks. I just look back at what I did before, how I am feeling, what sort of gains I've been making, and go from there. 6 weeks is a bit of a long time, but once you have a good pool of MRs and a feel for the program and the progress you are making, it's pretty second nature. For example, if for the past 6 weeks I'm making terrific gains, and each and every MR (lets say for back) I'm crushing week to week to week. I'll adjust my number upwards accordingly. So if 6 weeks ago I did 160lbs for 4 sets of 4 and failed on the 3rd rep of the 5th set of a cable row MR, but I've been really making great gains, I know I'm way stronger than I was 6 weeks ago, and probably up it to 170 and see if I can match or beat my old numbers at 160.
On the other hand if I'm struggling with lets say legs for example, and each week I'm barely beating old numbers. I'll either be more conservative in my weight choices, or abandon my current pool of MRs and try some new ones, just to do something fresh. It takes a bit to get the hang of it, but once you do, you can pretty easily see training session to training session and lift to lift where you are at. The auto-regulation that comes along with it becomes second nature. There is enough structure to guide you, yet enough freedom within that structure of lift selection, stretch selection, etc etc to guide yourself so you can continue to progress.
Hope this helps and let me know if you need any clarification.
