JBL QC???

TBH I can understand how things like this get past modern computerised/automated manufacture/QC. The units themselves are probably assembled mostly automatically without any human watching over, or if there are people invovled it could well be that the guy who sticks the PCBs into the cases doesn't know anything about what is actually on the PCBs. The QC tests themselves are almost undoubtedly just functional, rather than in-depth visual checks. Eg plug in the unit, if it behaves/performs as expected then slap a QC PASS stick on it without looking too closely at it, if not send it back. A component without solder might make a fine electrical connection & pass the functional tests, until it gets knocked around enough to wiggle free, so I wouldn't be surprised if something like that could go on working fine for years!

Here is the same thing on a Technics SL1200