It may have been correctly torqued the day you installed it but things do loosen. You're supposed to keep an eye on it over time as you ride.

Also, it's especially important that you retighten the lockring after the 1st ride with a new cog. Reason being, the torque from you pedaling is by no means replicable by a chainwhip and the final settling/ tightening of the cog under your pedaling will cause your lockring to no longer hug the cog and subject to loosening with road vibrations.