My answer is: I have no earthly idea and God bless Carlson Software for loving their customers and making it so easy!
In all seriousness, Autodesk’s pricing and purchasing model is changing so often and in substantial ways, I can’t keep up with it either.
I am not an Autodesk reseller so I can’t help other than to make referrals and give my opinion. But, I have a couple Autodesk resellers that I trust and who have helped me keep my own licenses of AutoCAD and Civil 3d straight over the years. They have also been hugely helpful to my Carlson customers needing to purchase licenses of AutoCAD.
Feel free to email me for a referral.