Not necessarily. It may be correct today and not tomorrow or even 10 minutes from now. Then again it may be correct all the time. Check the same sample with a calibrated refactometer and you'll know for sure.
, the ocean does not have a 1.023 SG
everywhere. Different oceans have different SGs and it varies from day to day....
Check out this article
"Different oceans have slightly different specific gravities. The tropical Indo-Pacific has an average specific gravity of 1.022 - 1.025. The Caribbean has an average specific gravity of 1.023 - 1.026. The Red Sea has an average specific gravity of 1.028 - 1.035. The specific gravity changes in each area are due largely to rain fall."