Muscle memory.

I remember when I first started wearing nappies properly around age 18 and I would have to stand in the same position for ages to start peeing. My sphincter would clamp shut straight away with the slightest movement. It was frustrating.

Now 13 years later after many many hours wearing I can basically pee in any position, walking, lying down, standing on my head etc. It's amazing how I have progressed but it has taken years to get where I am. When I put on a nappy I pee at the slightest urge like my brain associates my nappy with the toilet.

I have only worn occasionally in that last 7 months and my brain hasn't lost any of its muscle memory. I can still pee in any position and pee almost instantly when I put on a nappy.

Do you think if I stopped wearing for years my nappy wearing would still be engraved in my brain and I can pee on demand?

One of the "reasons" I cite for my diapers is a "diaper therapy" to fix my super shy bladder. It's worked for the most part but despite how long I've been at it I still consider it a "work in progress". I don't think stopping diapers will revert my condition though, as long as I were to keep up with use of public toilets. I think if I went back to only using the toilet at home, I may start to lose ground. My diapers aren't keeping my shy bladder in check, they helped me defeat it. (though they are certainly helping me keep it from making a comeback) So just keep peeing on demand when you need to and you should keep your bladder trained to obey.

It may not be possible to have completely no control. Even infants CAN control their sphincters long before they are toilet trained, they just chose not to. It's not any different than telling yourself to lose control of a finger. What you can do (oft with difficulty) is train yourself not to try to control it, i.e., just let go when you first feel the need to hold.