It is made easier for us to know what a Saint is the patron or protector of. That is why it is important to have so connection with him/her.
Still, we may not know sometimes, and we pray another, or directly God.
There is also instances that some things have 2 patrons: As a librarian, I may pray S. Jerome, but Lawrence of Rome is also the protector or patron of librarian. And I could have prayed S. Thomas Aquinas as a was a student.
If we pray “another Saint” it doesn’t matter in the end, since it all goes to God. A Saint won’t retain the prayers for him, or won’t listen because he isn’t the right one to be talked to.