For good reason.
Those commands are mutually exclusive. G90.1 calls for absolute mode in defining arc centers I, J, and K, while G91.1 calls for relative mode.
G91.1 is the default.
I have never added either, and I have processed a lot of circles and arcs.
If you call "G90.1 G91.1", as you have shown, you simply are re-selecting the default behavior.