Comparisons
NAD vs NAD+ vs NADH: What the Notation Means
NAD, NAD+ and NADH are the same coenzyme in different states. What the plus sign means, which form is oxidised, and why the ratio matters in the lab.
NAD+ and cellular energetics
NAD+ biology, the salvage pathway, the enzymes that consume and regenerate it, and the compounds used to study them: what is measured, where measurement is difficult, and which claims in this area rest on cell work rather than whole organisms.
Comparisons
NMN vs NAD+: Precursor and Coenzyme Compared
NMN is a direct precursor of NAD+, about half its size. How they differ in structure, how NMN becomes NAD+, what the human trial showed, and lab handling.