I worked on consumer and industrial electronic gear for over 30 years. I have seen unsoldered component leads in TVs, high dollar stereos and commercial equipment. Somehow, the joint didn't get any solder. Somehow, the simple physically-touching connection remained good through board testing, board installation, shipping and end-use installation. Then it worked for a while, sometimes years!
Some years back, Kenwood made a 2m mobile that
was notorious for the LCD display loosing contact with the
circuit board, resulting in a blank display. NASA had a Mars
rover mission fail. When it comes to electronics, *stuff*
happens, no matter the price, construction quality, or level of