Problems with ACS758 Hall Effect Current Sensors - Calibration and no Signal
I contacted Allegro they were really helpful which was pleasantly surprising.

The 200A has almost certainly failed. The 2.48v is within tolerance and the 2.33v is probably out. 

I've been able to better understand the datasheet sections on 0A calibration. "VIOUT(Q) may drift over the lifetime of the device by as much as ±25 mV." and there is an electrical offset voltage noted. @25C it's +/-5mv. It's +/-20mv between 0c and 50c. So still only 45mv. Even allowing for noise it's only 55mv. 

About 2.445V at zero amps would be the limit.