I find myself thinking "I wonder if that's an old line" about a lot of Eminem songs. He writes a lot, he has boxes of notebooks. I wonder how often he puts old lines into songs.
To the side of a pump, 0 to 60 hop in and gun it
Like G-Unit without the hyphen, I'm hyping 'em up
Gunit? They haven't been around in five year
". Feel the wrath of a psychopath slash ambassador of the valentines day massacre"
That album came out in 2005
Stuff like that, I wonder if he had this stuff saved up, things he had thought about years ago and finally used it.
There are a lot of other examples, probably better ones, that don't come to mind. I'll add more as I think of them.