Why Can't we Use Certain VO Name Calls?

[FarikoSilver_PSN]

I've noticed this for a while now that some are there for one name but not the other, or are there for Official players, but not for your Created player.
Is this a hard fix or what.

An example
Rhys Hoskins. I think he's officially on the Phillies?
in my rtts he's on the Reds now, and I got to play with him for a few seasons, Before My rookie contract ended and I got An Awesome deal from Arizona.

But I noticed His name is Voiced just fine, but when I went to Change my own name to that It wasn't available. I was Confused as to why.

The Same could be said for Silver.
It's listed as a VO name For A last name, but not a first.
I'm not sure if these are hard to flip around or add or what ever.
But I just noticed it with these two. I'm sure there are more that I didn't mention.