This is a feature request from Takeshi, piwikjapan.org webmaster. It had been requested by other users before: allow Piwik to import recent visitors, then old visits from the same visit and record them in the past.
When importing log files in random order, the visits are recorded for the last visitor instead of being recorded each day as we would expect. This happens because the "get visit" query does not restrict the "max date". So when recording an old visitor, if "new visits" from this same visitor have already been recorded, the algorithm would select this "new" visit row instead of creating a visit for the past date.
I will fix this by adding a test case and putting in simple solution.
This is follow up of #2584
In 56554b56911a1aacc155e0f837ddd12671db2f84: Fixes #3927 Adding future look ahead window to the SQL trying to detect the current visitor - fixing small bug discovered (in the tests) as a result of this fix