Well, I think releases that contains instrumental tracks and its price is cheaper are definitely new ones.
But why keep doubles and not replacing them? Good question!
I can't really recall full picture of her old catalog in our iTunes. There were actually many "incomplete albums" like they are providing ayu-mi-x 6 (instrumental version) right now.
And Ayumi Hamasaki/浜崎あゆみ mess belongs to Ayumi Hamasaki page anyway. Avex's flaw, I guess. Namie Amuro page has the same problem f.ex. in terms of artist name.