It had to be explained for you, perhaps, McTag, just as you and Oolong had to explain the more
obscure meaning of priest
. Wandeljw had to explain the meaning of his "new" word.
There's also no surprise in any of these examples. I dare say that even an educated wordsmith like you hasn't been from one end of the OED to the other.
The meaning is not random. Meanings are generated by the only method known to language for generating meaning, by people who use them.
Poetic license is a nonsensical term. Poets, authors, songwriters and the like have no more right to use language as anyone else. Accepted meaning is just that, what's accepted. The acceptance comes long before these "new" words ever hit the page of dictionaries.
As I mentioned, 'nominal' also holds a meaning of 'approximate', so it's not hard to see that things that approach an approximate success, can also be seen as being nominally successful, a nominal success, a test that while not outstanding, not 100%, served its purpose.
One dialect's boot
, surely an expanded meaning, is another's trunk
, again, another expanded meaning.