According to the video PBusardo put up on Molecule labs, there are inconsistencies in the bottle thicknesses and if they are filled by volume some appear to have less liquid in them. They pay someone to top up the bottles that appear to be low.
Some labs may not suffer the added expense just for optics sake.
I'd bet even if it appears low that if it was filled by volume and if it is still sealed, there is still 30ml. in there. Cheers.