I've heard of some parents telling that one of their kids skipped this milestone when they were baby. Some crawled before they learnt how to stand and walk.
My twin boys didn't really crawled. I don't know what you call this milestone...
I name it the Mowgly crawl as it resembled the way Mowgly(the jungle boy) imitated the way Baghera (panther)walked in the Disney's Jungle book cartoon.
However, my gals did went through the crawling milestone.
Do you observed the same in your child or children when they were babies?