Up to this point you have been working an increase at the start of every 4th row. It's worked as k3, slmx, M1R, and was first established in section 1. These are the shawl body increases.
In sections 1-3 it was possible to write the increases explicitly into the rest of the instructions, because the colour shift pattern was repeating over a number of rows that divided by 4 (there was a 20 row repeat in section 2 for example).
In section 4, the colour repeat pattern is worked over 18 rows, so it's not possible to write the shawl body increases in the row by row instructions (because first time through you'd be doing an increase on row 97, but on the second repeat through the shawl body increase lands on rows 95 and 99 etc...). So instead the RS rows say, "work in yarn A to 2 sts before y-marker" or "work in yarn to y-marker". This means EITHER work the start of the row as k3, slmx, M1R, if it's an increase row, OR just knit along if it's not an increase row.
I'd recommend writing the row numbers out and marking which ones will be shawl body increase rows. Then you can also add which rows are shift rows if you like. And the rest will just be worked in the basic knit or knit edges and purl the centre pattern with the colour changes at the markers.
I do hope that makes sense. Please don't hesitate to ask if I can help further.