It's not a very detailed pattern, so everything's there that's needed. In the event the knitter opted for a diff yarn, resulting in a diff gauge, number of rows is less helpful but all gauges can be measured (inches or cms).
Another vote for keeping track of rows. I use ledger paper. (I also knit both sleeves at the same time on circs to ensure they're exactly the same.) Just mark your 6 rows (vertically on the paper): K (inc), P, K, P, K, P and place a tick after each is completed. Repeat until the req's sts.
BTW, rather than doing your increases in the first and last, you might want to do them in 2nd or 3rd. Doesn't impact your selvage sts when seaming.