Which, again, would render the gas detector completely useless.
So, there are two scenarios :
A) Prior to TUC all cloaks could be seen through if people looked for gas emissions and nobody found that glaringly obvious problem until TUC and then it was fixed
Or
B) The gas dispersion was never fixed and no other vessels sensors were ever recalibrate to detect it.
Either one presents the people involved as pretty dumb. I prefer to drop it in the same box as the genesis device, trans warp beaming, Khan's blood, and so many other inventions that show up for one moment and are never mentioned again because they'd cause inherent changes to the franchises formula that nobody wanted.