There are stories out there about people in virtually every field, who didn't master the basics of their field. Famously, employers like Google and Facebook give "coding interviews" to computer science graduates, to find out if they can actually program. Truth be told, you can sneak your way through a degree program with gaps in your training, and it doesn't happen all that often, but it can happen.
I know a few people who are Berklee grads, and many more who are music school grads. One got through a couple years at Berklee before his reading problems caught up with him. They were partly cognitive. He could see perfectly well, but he couldn't see music if it was on one side of his field of vision.
But also, there are different levels of reading. There's reading in a theory class, there's sight reading, and there's sight reading difficult material cold in a chaotic gig situation. Like many other skills, reading ability atrophies if it isn't used, and there aren't much chances to keep up with any reading, much less treble clef, on the bass. I have been extremely lucky to have played in bands where reading was necessary, so I have managed to keep up my reading chops.
But I struggle with treble clef. Right now I'm trying to learn how to play jazz on the cello, and I decided that I would read everything in treble, just to get that portion of my brain working once again. I haven't read treble and tenor since high school.
There was a bandleader in my locale who wrote his trombone parts in tenor clef, and it always took players for a loop because they thought it was just going to be an easy gig playing dance music, and very few of them had kept up with tenor clef.
