Flaws in Lord of the Rings... Yes in the book.

[Nilpaurion Felagund]

How could a ring be a literal foundation of anything, much less a mountain of iron, as Barad-dûr is described? It has to be metaphorical.

"The Dark Tower was broken, but its foundations were not removed; for they were made with the power of the Ring."

"they" is ambigious; it could refer to the Dark Tower or the foundations. The entries from the Tale of Years that you quoted points to the latter. He built the actual tower first, with an actual foundation, but it had no foundation for domination and terror until the completion of the One. Didn't you notice that Sauron did not attack his enemies in the Second Age before the forging of the Master Ring?