Just as another T26 data point... I started in October, but for the first 2-3 months really only was able to fit in 1-2 sessions per week because I also started in a twice weekly masters swim program at the same time. Since February, I have been doing the T26 workouts pretty faithfully (2 A, the C, and the B workout about half the time), and I stopped doing the masters swim program. Current volume is around 15,000 yards across 4-5 swims, per week.

My swim times have definitely improved over that time. I dropped 50 sec in my 1k time trial from January to May, and probably 1:30 in an extrapolated time since October. So my swimming has definitely improved. While I love the T26 program and plan on sticking with it, I do miss having a swim coach on deck as I think there is a lot of value in having that feedback, particularly with mechanics. So that is important, and I'm currently trying to figure out with my schedule how to add that back in.

But honestly, I think the biggest benefit I've experienced to the swim volume I took on over the winter has been an improvement in my overall aerobic fitness. My run times have dropped, even though I'm not even running as much as I was prior to starting swim training.