I do not know the procedure followed by EasyEDA, LCSC or JLCPCB to verify Symbols and Footprints. User contributed parts however always bring up with a warning that they should be checked before use. This is because they are not checked by EasyEDA. Symbols and Footprints that I have contributed are checked against the original manufacturer's datasheets but even so, some turn out to have mistakes that I have missed when checking them. In any event, checking Footprints against the manufacturer's datasheet is recommended to avoid, or at least minimise, the chance of any mistakes.

@andyfierman That's the question. What are being verified? One thing for sure, as you mentioned, that is verifying on paper against the datasheet. I don't think this is good enough for an official "verified" part. When I finished a pcb design, I reviewed the pcb and verified all the parts. Next time I may improve some of the footprints. For through hole parts, you may just try to push the part into the pcb. Some of the easyEDA DC jack footprint holes are way to large for example. More definition is needed. For example: this footprint is verified against datasheet by ..., but not verified by assembling.