IMO the charger doesn't need to know anything except the battery voltage now and then later. The battery will take its own time for the voltage to rise to whatever the charger's trigger voltage is.
If the initial battery voltage is already spiked up from say another charger being on first, or if it was on then turned off, then turned on again for some reason, the battery's SOC is still low, but the charger just goes to work and eventually the battery's SOC will rise and its voltage will go up some more until it gets to charger set-point trigger. The charger doesn't care how long it takes, the battery decides that.
If the battery's SOC is really higher already, then the battery voltage will spike as soon as the charger is turned on and reach the high trigger right away. So an Iota, eg, will then do its 15 minutes of bulk and drop to 14.2