Or, what was meant by that is that when you eat a Devil Fruit, you learn what ability it has, and you call it according to the ability. Not that you literally just know the name of it by eating it.
In the case of Kaku and Kalifa, their devil fruits were unknown, and not in the Devil Fruit book.... So how did they have names before Kaku and Kalifa ate them? Who named those Devil Fruits when they exist in no form of text anywhere? Or do Devil Fruits just name themselves? Lol
If you eat a fruit that makes you stretch and act like rubber, then clearly you would assume you ate the Rubber fruit. If you ate a fruit that turned you into a Giraffe, then clearly you would assume you ate the Giraffe Devil Fruit....
All Spandam said was you learn the name of the Fruit, when you gain its power. Not that you learn its name just by eating it.