Beuhlah I am one of the 4 leaders for the Sourcerers' Challenges.
One of the problems with measuring how much is done is that for every corrected profile there are new profiles added to the tree that may not be properly sourced.
So the way I look at it is to see the number of profiles that have been corrected over time.
Here are some stats and reports to do that...
1. On the Project Page we track years of sourcing https://www.wikitree.com/wiki/Project:Sourcerers
there is a link there to see the archive which is located at https://www.wikitree.com/wiki/Sourcerers_Challenge_Archive
It shows from July 2015 through August of 2016 26,241 profiles sourced. I just realized these stats were not kept up so will contact the team and see what we can do to update this.
Currently for 2018 (this is from a spreadsheet the leaders maintain) January through Sept (Oct data has not been finalized / entered yet) 77,443 (does not include Source A Thon)
From same google sheet total for 2017 shows 86,929 and does not include Source A Thon data
2016 shows 43,973
And July 2015 through Dec shows 8,104.
So a total of July 2015 through Sept 2018 is 216,349 not including Source A Thons (at least I don't think it does...) will try to verify that with the team...
The two Source A Thons did even more but I really have to do some looking to come up with those stats...
Have sent an email to my co-leaders about updating the Archive Page.
2. Another way I look is to go to the Data Doctor reports for unsourced profiles https://www.wikitree.com/wiki/Space:DBE_Unsourced
this list is broken down by locations. It shows you the time period and newly added profiles that are showing as unsourced. If you are interested in a specific area you can print these and save them and check back to see if the numbers are whittling down. These will show all sourcing whether it is part of the Sourcerer's Challenges, the Source A Thon, or just folks doing their own thing. So as the numbers diminish you get an over all effect.
3. You can also look at the overview for the Data Doctors Report for errors that are included in the unsourced report error#s 131, 132, 133, 134,802, 803 (note Ales works some wizardry to come up with others that are included in his unsourced list besides these listed errors) https://www.wikitree.com/wiki/Space:Data_Doctors_Report_2018-10-28
Hope that helps.
In my mind it shows definite improvement.
This years Source A Thon showed 72,713 improved profiles.
2017 Source A Thon showed 53,245 improved profiles.
So I am pretty confident those are not in the totals I had above!