Camera Specifications for sensitivity maybe quoted as 0.5 lux @ F1.4 Typically all sensitivity checks should be carried out at a known lighting level ( the light is measured on the subject or as reflected on the camera pickup device “the CCD”) if lighting is measured on the object it should be known what reflectance the object has e.g a chart with a calculated 89.5% reflectance will reflect 89.5% of light upon it. so 0.5 lux is the light level that it can still get a acceptable picture from, when using a lens with an Fstop of F1.4 ( Fstop can be considered a factor of losses of the light through the lens glass or plastic whatever may be the case due to factors such as the opening of the lens that lets light through).
If a supplier left off the reflectance associated with the cameras specs and if its specs were based on 100% reflectance. It could be said that as objects do not reflect 100% of light upon them unless they are gloss white then the sensitivity may be overstated. Also if the lens used is not known of what its Fstop is or a Fstop higher than that quoted in the camera specs is used then the sensitivity will be overstated.
Take the case of Dome cameras do the specs reflect the actual lenses used, again this may be that you are not comparing apples with apples. best to have a shoot out or put your trust in someone with the experience to have experienced the the differences in products. CCTV industry has many newcomers and they can not have the wealth of instant experience.