"All the same, we bid you spare the food,' they said. 'Eat little at a time, and only at need. For these things are given to serve you when all else fails. The cakes will keep sweet for many many days, if they are unbroken and left in their leaf-wrappings, as we have brought them."
And here is a time when Tolkien is refering to them in the story:
`Did you see them again, Mr. Frodo?' asked Sam, as they sat, stiff and chilled, munching wafers of lembas, in the cold grey of early morning.
Oh I know. I was just commenting on the fact that Tolkien would know something and cause confusion by not "telling" the characters...