The scientists who figured out this technique, that uses existing hardware onboard Curiousity and other spacecraft, said the same thing. It could only detect life that was still alive or had died within hours. And they considered it extremely unlikely it would find existing life on the surface of Mars.

Extremeophiles are tough little critters though.

There was one of these instruments on the Titan Huygens probe in 2005. Damn shame no one knew this technique then. It also could be useful for future missions flying through water geysers on Enceladus and other moons. This instrument is not on either of the enroute Jupiter probes.