The Authors, as BR said retain the order entered.
There are also many cases where the Author order is contractual

Big name Author gets their name Higher or Bigger (same as with Actors) that their co-writer. (and it may flip further into the series. The BnA may just be helping a newbie get noticed or they started, then said 'run with it Kid'

)
and underneath the skirts:they are just a (sort) key numbers to the Authors table, 23,45,192. And those numbers were assigned the first time a Author name appeared in YOUR Library.