Updating baselines with multiple open projects

Hi All,

I am having trouble understanding how the baseline updating works when multiple projects are opened at the same time. 

I want to batch export data on several projects. After opening all the projects, when I want to reassign the baseline, it only allows me to reassign/update only one of the projects baseline. Shown below:

Even if I try to change the project and then change the baseline and rerun the schedule, it still picks the default project and baseline. So, I have several questions:

1. If I have multiple projects opened at the same time, how does reassigning baseline works. If it only allows me to change baselines for one project, how does it impact the remaining project baselines? Does p6 recalculate other projects' schedules based on their individual most recent baselines, or keep calculating with baselines that were assigned when these projects were opened individually.

2. How does this process take place when I have projects with different baseline data dates?

3. If I want to create a report for multiple projects with with most recent baselines, do I have to open them individually and reassign/update baselines individually and run a report? Or there is a way to run a batch report with all of projects having their baselines updated to the most recent data dates?

Many thanks!