Forklift battery - specific gravity vs trimetric

Hi,
Just recently started using a new GB Industrial battery that is 804 AH (20 hr rate) @ 24 volts. Am nearing the end of the second cycle and am noticing a possible trend. They sent a paper with the battery giving the specific gravity readings for fully charged (1.285 to 1.295) and 80% discharged (1.170) and 100% discharged (1.140). After going for several cloudy days and monitoring the trimetric SOC meter as well as voltage and specific gravity, it is becoming more apparent that the voltage and trimetric kind of agree that the battery is 30-35% discharged (resting voltage is ~24.4 and SOC meter says 70%, while the temp. compensated SG indicates the battery is substantially lower (~1.200). According to the SG figures we were given, 50% DOD should read around 1.215 on the hydrometer. But resting voltage at 50% should be 24.1. I have tried finding all the SG charts I can and there seems to be a lot of variation amongst them. I am just wondering if my assumption that 1.215 is 50% is incorrect. Does anyone have any experience with or info about forklift batteries that might shed some light on why I am finding this variance and how I can accurately know when I have reached 50% DOD?

Many thanks!