He doesn't use the slates? My husband uses the slates and checks off each skill as he goes through it for every type of class he teaches. The other instructors I've worked with do the same.
In contrast to your experience, I rarely see an instructor use slates for the skills for the CW dives. If you have done things a lot, you get into a routine. When instructors do refer to the slates, they skim them, just looking for the key words to remind them of the name of the skill. They may not have read the actual words there for years. I am pretty clear on the wording of the skills because in the past few years I have written articles on the standards and engaged in debates about them.
In some cases, they are following routines developed over many years, not noticing when things change. How many instructors are still insisting that students follow the exact form of a fin pivot, not realizing this was changed years ago? I recently heard an instructor say that for PADI, buddy breathing is an option, even though that, too, changed years ago. When I switched shops a while ago, the manager came to me because he noticed that I had not been placing the students' knowledge reviews in their student record files. He was surprised when I told him that PADI had removed that requirement a number of years before.
In other cases, the instructor is following what they were taught by a more senior instructor when they were starting out, not realizing that what they were told to do was not in keeping with standards. This can be especially true if someone serves as either a DM or an Assistant Instructor for a period of time. You imitate what you first experienced, not realizing that it is not a standard practice. I encountered an instructor who taught most of the skills with the students not wearing fins. He had apparently learned that from the Course Director who ran his IDC. It made it easier for students to kneel while doing the skills. He was surprised to learn that it was not standard practice. The practice of teaching students while they are on their knees is so firmly entrenched that there are many who still insist it is a required standard, even when PADI has made it perfectly clear to almost anyone's ability to read and think that it is not required.
It should not be surprising to know that this happens. In 1970, education researcher John Goodlad attempted to compare different educational programs to see which were the more effective in student achievement. He identified schools using different programs and compared their achievement. Fortunately, he was thorough enough in his research to go into the classroom and watch the teachers as they worked. He discovered that he could not compare the programs at all, because once the teachers were in the classroom, they taught the way they had always taught, often in direct contradiction to the programs they were supposed to be implementing. Going further, he found that teachers tended to teach the way they had been taught themselves or the way they had first learned to teach the subject, regardless of anything different in the way they were supposed to be teaching.
