So im going through this right now with the Hanna tester. ive been documenting my unscientific findings in the thread here on the hanna official sponsor forum.
All methods should be verified and/or calibrated, and if you think a device reads low, you can make your own standard, or buy a different brand standard.
I persoanally see no reason to not target the whole ocean average salinity of 35 ppt, sg ~1.0264, but our creatures are Ok in a pretty wide range of salinity.