Live data stream shows you total fuel length in ms - what is driven to the injectors after all overrides are factored in.Both, because if I ever decide to run E85 I would have to know when injectors are maxed out.
Look at the fuel cell for a given load/rpm. The values are uS/58 or uS/50, depending on the firmware level.
When the change occurred I don't know (maybe DDFI-3).
As an example, if your map cell at Load:15/RPM:1150 is 66, then 66*58=3,828 us = fuel length of 3.828 ms.
"Wide open" (the way I think you're trying to define it) can be estimated by looking at the source fuel maps, finding the largest cell value, then factoring in the all the possible multipliers that could happen (engine/air temp, front cyl temp, open loop, learned fuel, battery voltage) depending on the actual operating condition.
It goes without saying that you should re-tune with dual o2 sensors after making fuel, timing, or mechanical changes.