TDC just to be clear, I'm saying your idea definitely isn't the end all be all when it comes to knowing your gun is loaded or not. I don't often say there is only one valid "way" but when it comes to knowimg your gun is loaded, there really is only one way. Its like pregnancy, there is only one way that is 100% effective, don't ####. Same with looking at your gun. Sure you could induce a stoppage if you don't put the slide back properly but same thing if your mag doesn't go back in right. mags not feeding right does induce stoppages including messing with mag safeties on some guns (Smiths, Berettas for instance).
As for knowing your mag isn't working, well the only way to know that, is when it stops working. You can inspect them all you want, but springs break, followers break, mag lips come off and mag spines break at the most inopportune moments. Sometimes while shooting, and sometimes during insertion. I've seen of those things happen, had them happen to me too. Hell baseplates come off during firing and loading, rounds shooting up through the slide when feed lips let go, you name it. I've seen guys put a stripper mag in, rack the slide take out the empty mag put in a fresh one and still get a "click" no bang when they draw. The live round being on the ground after not actually being fed or jumping up out of the slide during feeding due to loose lips or broken ones. I've seen pieces of dirt/brass/whatever hung up in the inspection holes on a pistol so it looked loaded and I've seen the same crap hold extractors out after a gun was cleared making it appear loaded.
The absolutely only way you are going to know if your gun is loaded is if you actually see the round in the chamber. It really is that simple.