As the plan of a Jesus to be was the firstborn of God's inner...

As the plan of a Jesus to be was the firstborn of God's inner creation, that puts this plan before Adam.

All things were created on account of, for the sake of the future Jesus. Col 1:16

Inter...........firstborn of creation because in him = "for this reason" - all things were created, on account of, by reason of him and for him Col 1:15, 16.

That is as per Inter, keep in mind I don't think the originals had verse numbers etc and it just flowed.
So, are you seeing Why he is referred to as the "firstborn" 'because'

Hence a Jesus to be had to be the first creation thought.