[millstone]

We should distinguish between quantization, and "discrete particles with distinct properties." For example, the photoelectric effect demonstrates that light is quantized, but individual photons have no distinct identity whatsoever.

"Number of particles" is an observable like position, momentum, spin, etc. It is a quantum property which may or may not commute with other properties, and occupies the same conceptual space.

[nine_k]

Number of quanta is observable. You can count photons.

OTOH it does not imply that a photon is a "particle" in the same sense a breadcrumb is, with a well-defined diameter, shape, or borders. It is a portion of energy of electromagnetic field that was sufficient to yank an election from a photo element's crystallic grid.