Description:
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I tried make an diff in 1899-01-01 and 1970-01-01 and don't return only year difference, return months, days, hours, minutes and seconds.
I made some tests, and date before 1915 this happend.

Test script:
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var_dump((new \DateTime('1912-01-01'))->diff(new \DateTime('1915-01-01')));

Expected result:
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object(DateInterval)[2405]
  public 'y' => int 3
  public 'm' => int 0
  public 'd' => int 0
  public 'h' => int 0
  public 'i' => int 0
  public 's' => int 0
  public 'weekday' => int 0
  public 'weekday_behavior' => int 0
  public 'first_last_day_of' => int 0
  public 'invert' => int 0
  public 'days' => int 1095
  public 'special_type' => int 0
  public 'special_amount' => int 0
  public 'have_weekday_relative' => int 0
  public 'have_special_relative' => int 0


Actual result:
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object(DateInterval)[2405]
  public 'y' => int 2
  public 'm' => int 11
  public 'd' => int 30
  public 'h' => int 23
  public 'i' => int 53
  public 's' => int 32
  public 'weekday' => int 0
  public 'weekday_behavior' => int 0
  public 'first_last_day_of' => int 0
  public 'invert' => int 0
  public 'days' => int 1095
  public 'special_type' => int 0
  public 'special_amount' => int 0
  public 'have_weekday_relative' => int 0
  public 'have_special_relative' => int 0