Hello,
I used to export my data on daily basis for several years now.
When I look back at my last year data today in piwik.
They Changed.
Any clue of new ways to count data ? or modifications ?
Can you let me know what changed and do you have any screenshots of before / after?
Please send me them in a private message.
Have a great day! 
Hello
EveryDay, i write the number of sessions in an excel file.
When I come back to what i wrote last year, and compare it to piwik now, numbers in piwik are 5% up on average.
Does piwik keep computing data after the last day ?
Was there a correction ?
Maybe there were some long sessions?
Please have a look at these articles, generally you should see data 30 minutes to an hour after the session is over.