That's not my understanding but admittedly I may be incorrect. What you're referring to is how gold/platinum certification is figured. If Guns N' Roses has 500,000 units shipped to stores, but only 100,000 are sold, it is declared gold. I believe charts rely on soundscan numbers which count the actual number of albums sold, upc scanned, monetary exchange, etc. Of course that in and of itself is difficult because not all record stores are attached to a soundscan system so they used to have guidelines that 1 CD sold at Best Buy actually accounted for 3 to make up for all the small shops that don't report.
Some online retailers charge you the second you preorder. Amazon doesn't. Honestly, I'm not sure if any of us knows exactly how this is figured anymore since the industry has been upended.