Even so I would not really trust any monitor that shows SOC. I like to cross-check anything I can to see if it reads right. I use resting battery voltage tables for SOC to cross check the AH count for SOC to see if they "match' within reason.
The Victron ISTR has an automatic "sync" for when it thinks the batts are full. This is where monitors get out of whack for whatever reason, so a cross check is useful. I don't trust automatic anything.
It is like a digital voltmeter that starts to show higher voltage when its battery gets low. It is insidious so you don't notice it is getting off -kilter until you get a cross check with a different voltmeter.