In Chapter 980 Zoro makes his appearance by cutting the top off one of the Live Floor’s towers.
Since then, the severed tower has had a constant presence in the backgrounds set in that part of Onigashima in a bunch of chapters, showing Oda never forgot about it. Here’s a good overhead shot including it from Chapter 1006.
And now, almost 60 chapters after it was first severed, Oda brings the severed tower to its final destination by having Law use it to attack Big Mom!
We can even see that the underside of it matches the overhead shot from Chapter 1006.
It’s a small thing. No one would have questioned it if the broken tower had just disappeared, or if Law had just dropped some random debris he picked up instead. But this kind of attention to detail is what makes One Piece what it is.