Thanks for the feedback and info. No doubt the length of you levers (aka: upper arms) contributes to the difficulty you have with pull ups. Those with short upper arms definitely have an advantage. There’s a reason gymnasts tend to be small.
I’d say a 50% increase in endurance and doubling of your weighted pull ups represents an unqualified success. This is your first cycle. Do this another time in a month and and you’ll see more gains. Age has little to do with this. I have know 60 year seasoned climbers who saw great gains with this program.
I like to use increasing weight in each set. I find that way my nervous system gets fired up a bit more on each set and I recruit more fibers and feel stronger as I go. In 4 sets of two I’d propose going 15kg, 17.5kg, 20kg, 20kg. It has a kind of warm up effect.
There is no reason to not use this prior to the Ice and Mixed plan in the fall.
As for the typo you mention. There is no ‘right’ or ‘magic’ progression. I laid this out with a progression. People have modified it and seen great success. Its just a template.