I've realised there is no fair way to do this with the information available. I can't use daily averages as they don;t seem to have an option to display them. If I use peaks, that is going to show a better scenario than is real, if i use troughs that will show a worse than. As either method completely disregards the rate of change before and after each point (the last 5 days have high peaks, but they are very steap, meaning the average over each day is much lower/people aren't playing long). Basically not having every data point means anything I choose to use will be open to accusations of using biased points. I'd also have to attempt to explain what each regression line actually represents (linear, polynomial and exponential) what R values mean.
I will still show the overall trend line bases on the peaks over the entire life of the game though. As that does show how this update is performing to previous.
EDIT: So this is what we have when looking at the entirety of 7DtD and the last year. Red dotted lines are best fit polynomial regressions as they best display the change in trend over time. Blue dotted line on second image is linear regression which shows average trend over the period (there is no point doing linear for all time as anything that starts at 0 will always be positive). As you can clearly see the game has been trending down since July 2016. Even with the current spike, they haven't hit the same numbers as previous update releases, despite the extra copies sold.
Yes, the user base is currently trending up as it should be, but it still hasn't hit the same peak as this time last year. And while there may have been a sale last year there was no patch to bring old players back, so there was not even a proper peak at that period of time. As such when you look at the overall trend for that period (blue line) it is still trending down for the whole period. Again, despite how many extra copies have been sold in the last year.
If we were to put these metrics alongside sales statistics and do a multiple regression then this would be a much worse image for the state of the game. But thats too much work and tbh I can't believe I bothered to do this.