Who knows? Have you ever been taught an undocumented procedure by the expert and been told to use it regardless of what the manual states? Happens all the time? Is a pilot in a position to affect Boeing beauracracy?

Sorry but how could Boeing design any plane if they can't assume pilots will follow the manual or any checklists?

By including features in the manual. The alternative is that they don't, people rely on the features, they change the features without notifying anyone, and when shit goes wrong they can say "It wasn't documented: shouldn't do that".

The real question here is how commonly this feature was used. If it was common, then not putting it in the manual is a big problem!