Think of them as relative indications of feature size and of spacing between identical parts (arrays if you want to use a software analogy), so even if an actual transistor will not be 10 nm or 14 nm their relative sizes will relate on one axis as 10 nm to 14 nm. Keeping the numbers from a single manufacturer will definitely aid in the comparison.

There is a ton of black magic going on here with layers being stacked vertically and masks not having any obvious visual resemblance to the shape they project on the silicon because of the interaction between the photons / xrays and the masks due to the fact that the required resulting image is small relative to the wavelength of the particles used to project it.

There is a super interesting youtube video floating around about this that I highly recommend, it's called 'indistinguishable from magic':

https://www.youtube.com/watch?v=NGFhc8R_uO4

It's up to date to 22 nm. Highly recommended.