Jo Sharp Desert Garden gauge

I do not swatch - I know, knitting heresy, but every time I do I get the gauge that's on the label. And changing needles change nothing. So I do not do it. But sometime a yarn yells: "Look at me, do you believe that gauge? Don't be fooled, they were on drugs when they wrote that." Jo Sharp Desert Garden is one of those yarns. 18 sts / 4"? I looked at yarn and thought: "No way". So I did swatch. Guess what? 15 sts / 4".
I never change needles, unless I hate the drape I am getting. If I like it, if it is not broken, why fix it? And besides that, I can count and add, even multiply so here is what I am doing for Nothin' But a T-shirt - bust size 40 inches.

I casted 75 stitches (duh!). Decrease for waist shaping: I need to decrease 6 sts, so 3 rows of decreases instead of 4. Increase for bust shaping: I need to increase 8 sts, so 4 rows of increases of 5. I have a total of 77 sts at this point, and I need to have 59 sts left after the armholes, so my armholes decreases will be 2/4/3=9x2=18. Neck: knit 20, bind off 19, knit 20. Neck shaping ..... I'll figure out later, I have knitting to do!