Either count your slip knot as a stitch or don't and take it off, but don't 'adjust' the stitch number because of that one stitch.
"K15, inc2, K15, slip, K2tog, psso requires 33 sts to start"
does not, it takes 34 sts because the sl k2tog psso uses 3 sts, decreaseing to 1, but the kpk into 1 st makes up for it so your incs and decs balance out.
"K5, pm, slip, K1, psso, *K15, inc2, K15, slip, K2tog, passo, repeat from * 6 more times, end last rep with slip, K1, pm K5"
There's 7 sts at the beg of the row, repeat the st patt of 34 sts 6 times, then repeat it again but instead of 'k15, sl k2T, psso' you're going to 'k15, sl 1 k1, psso and k5. So that last repeat is only 33 sts plus the 5 at the end and 7 at the beginning. I get 249 sts, same as you start with.
sue- knitting heretic