I think the OP's premise is a bit of a stretch, to say what Riker found unexpected was just the deafness. Clearly there's other seemingly remarkable things going on with him.
It does seem weird they wouldn't have had foreknowledge of him, given how renowned he is, but maybe with how diverse their universe is, it just doesn't come up much.
You wouldn't necessarily feel the need to pass along that Troi is empathic in a briefing to a mission she was being sent too, because of how common telepathy is in their reality (even though they DO mention it... A LOT lol)
You can't have it both ways though. Either his state is noteworthy, making it unbelievable that no one noted it before meeting him, or his state isn't noteworthy enough to mention beforehand, & their surprised reaction is out of place
It does seem weird they wouldn't have had foreknowledge of him, given how renowned he is, but maybe with how diverse their universe is, it just doesn't come up much.
You wouldn't necessarily feel the need to pass along that Troi is empathic in a briefing to a mission she was being sent too, because of how common telepathy is in their reality (even though they DO mention it... A LOT lol)
You can't have it both ways though. Either his state is noteworthy, making it unbelievable that no one noted it before meeting him, or his state isn't noteworthy enough to mention beforehand, & their surprised reaction is out of place