Question about pattern instructions

[rebglass]

I am finishing up the back of a sweater, and am to the "shape neck" part of the pattern. Instruction is to:
" cast off 15 sts, patt until there are 19 sts on R needle and turn, leaving remaining sts on a holder.... Cast off 4 sts at beg of next row.
Cast off rem 15 sts."
I get it up to the 2nd cast off part. I don't know why I'm not just told to cast off 19 sts, and I'm afraid there is something I'm missing.
It may not be a big deal but I would like to get it right.
Thanks
Rebecca

[suzeeq]

Just do it as it's written. The 4 sts may be for the dip at the back of the neck that needs to be a little lower than the shoulders and it should come out a row lower.

[rebglass]

Just do it as it's written. The 4 sts may be for the dip at the back of the neck that needs to be a little lower than the shoulders and it should come out a row lower.

that's it, though, the 4 sts don't come out a row lower. As the instruc are written, I'm to cast off 4, then 15 in succession. I just wondered if I should do the 4, then finish the row, then cast off the remaining 15 on the next row....

[suzeeq]

I just wondered if I should do the 4, then finish the row, then cast off the remaining 15 on the next row

That would work better, and I think it's what it means, though it wasn't written correctly. You would always bind off a shoulder at the beg of a row.