I've run into this several times and it is somewhat frustrating. It's like finding a recipe on a blog that you want to try, and the measurements say 1 package of cream cheese, or jello, or butter, but not how many ounces or what size of that item.

I'm experienced enough that I can usually figure out the quilt pattern, but I feel bad for newbies who can get frustrated and give up.

I have found errors in a couple of books and I notified the writer. She blamed the publisher. I made notes in my book so I wouldn’t make the same mistake again.

I just had to do this this morning and it can be frustrating. I kept wondering to myself why this wasn't working as the directions stated only to discover after several hours of searching I figured it out on my own. The directions said nothing about a minor detail that made all the difference. The first part of the project will have to finish off the way I originally made it and from here on out I will do things the way I since discovered. Nothing like being brain dead! Hours of reworking the pattern.
I hear you with the frustration of having to rewrite someone else's instructions. Best of luck.

I get out my graph paper and re-draw the pattern as well as I can. Sometimes I have to change dimensions a bit, but usually end up with an understandable diagram.

I have had to change measurements on some patterns. Most of the time I make up my own.

I"m not sure I've made many things that I totally followed the instructions anyway. I was notoriously bad about not making garments according to instructions. One of my friends once asked me if I had ever made a pattern without changing it.

Seems so many patterns have errors that I never trust them. Find the same with crochet patterns.