So... SDI has a similar thing called Advanced Adventure that is like the PADI AOW you described... I believe SSI calls it the same thing. Though with SDI it's not entirely pointless... it does expose you to navigation, deep, and other stuff. When you get Advanced Adventurer via SDI it does extend your depth.
SDI OW - 60 feet
SDI AA - 100 feet
SDI Deep - 130 feet
I thought I heard that most of the agencies only accept two specialties from others... that may differ from agency to agency.
Those depths are for training courses only.
Every OW diver is certified to 130 ft - the accepted recreational limits.
When I taught as a YMCA instructor, OW included gas management and rescue skills as well as emergency deco procedures.
I ran into many people who thought that their OW card meant they could not go deeper than 60 ft. And if I were acting as an instructor or guide, I would not take an OW diver deeper than 60 ft.
And when I got certified as an OW diver, I was given the impression that to go deeper than 60 ft, I needed AOW or Deep. The same instructor told me I needed AOW or night to dive at night.
Neither of those was true. Those impressions were designed to sell additional training.
Nothing stops an OW diver from diving to 100 or 130 ft if they have the gas and experience to do it. When I taught OW, I made sure that if my students decided to do this, they had the skills and knowledge to. I strongly advised them to work up to those depths over a number of dives. But they knew they did not have to come back to get a card to do them.
If they wanted to, that was fine, and I made sure the AOW class gave them more knowledge and skills.
Ops requiring AOW to allow you to dive on deeper sites is not about making sure you know what you are doing. They are covering their butt so that if you do screw up and die, it's on you. They can say "He had the card."
So, those courses are supposed to give you more knowledge and a few extra dives with an instructor. But they don't "extend" your depth. You were always certed to 130 ft. And now you can do that in other training dives. But you don't need it to do them.
As for the night diving I mentioned, what do you need to do that? An underwater flashlight. Period. It helps to know how to use a compass or a line and reel, but you always have the option to pop your head up to see where you are.