Sizing questions with a particular pattern

[Rags84]

So I'm making my second sweater. My first one, despite it being a size large (and that's the size I usually wear), it's a VERY SMALL size large. So, the lady at the knitting store was kind enough to measure me and tell me how many stitches to cast on since that size isn't one listed in the book. She told me once I cast on that many stitches, I should just follow the directions. However, when I got home, I continued to read further into the directions and realized some other numbers will need to be altered too. The knitting store is kind of far so I won't be going back very soon so I'm hoping someone here can help.

Here are the EXACT directions.

With size 7 needle, cast on 78 (86, 94) stitches and work in K1, P1 ribbing for 6 rows.
Note: 78 is for a size small, 86 is for a size medium, 94 is for a size large.

Change to size 9 needle and work in st st until piece measures 11.5" (13", 14") from cast-on edge ending with WS row.
Bind off 4 stitches at the beginning of the next 2 rows.
Bind of 3 stitches at the beginning of the following 2 rows.
Then decrease 1 stitch at each edge every other row 2(3,5) times until 60 (66, 70) stitches remain.

So I'm good up until the last portion where it says:
Then decrease 1 stitch at each edge every other row 2(3,5) times until 60 (66, 70) stitches remain.

Now, those numbers make sense if you cast on one of the original options for the sizes but since she told me to cast on 110, I probably should end up with more than 70 stitches but my question is...how many should I have? I assume I am decreasing more rows since I have more stitches to begin with.

I hope this made sense and someone can shed some light.

Thanks!