When one takes a file from a software and uses it somewhere else,
without change. Then the same file has different copyright
years. To me that would be to confusing. That is why I can not
believe the following statement.
I am unsure what the confusion is about...
When the second project updates something, it is the whole work that
the copyright years apply to, not just a specific file, so the dates
for all files should be updated in that second project. Since file was
originally written for a different project, it is logical that it will
have different copyright dates -- it cannot possibly have the same
dates as the second project (unless, ofcourse, both projects have been
updated in the exact same years).
The original project from where you copied the file might not have
been updated, so no change in copyright dates for that particular copy
of that file.