Tracking inventory for an item that is limited edition

[Grggry]

I have created an item library. A few of these times are limited edition linocut prints. I was able to add an inventory count to one of this items, BUT I am unable to add it to the other two listed for sale.  What am I missing? nothing in the support article helps me that I can see.

[Grggry]

 I was able to add variations to those limited editions... But do I need to add a limitation inventory count for a singular item