You are right LED bulbs only work one way, connected up the wrong way round they will not light up.
Nothing landy but just a little recollection
When I working in the Chemical industry, we changed all our control panel alarm lights to LED and we had a box of spare bulbs to change if one failed, some of the guys would put a new bulb in and try it and if it did not light up they binned it thinking it was a dud that had been put back in the box and kept on until they by chance fitted one the right way round. At the start of my shift I used to dig them out of the bin and try them and usually found one or two good ones in the the duds. (It was a safety routine to check all your alarm lamps at the start of every shift) they were all educated about this when maintenance dept started to complain about the number of bulbs we were going through. They also complained about us calling them bulbs, lamps, lamps, lamps they call them lamps they would say.