What is this small number on the top right of an IAP?
It is the year followed by the day of the year of the last ammendment to the chart. If there have been no changes to the chart since it was first issued, this space is blank. In this case the chart was revised on the 171st day of 2019. If you look at the bottom left hand portion of the chart, the date shows the last time the procedure was revised e.g.—17AUG17. Apparently there were changes to the chart (obstacles,  name of the airport, typos in the notes, etc.) that did not affect the procedure, so the dates are different.

Refer to the Aviation Chart User’s Guide.


  The Date of Latest Revision is shown on the top margin above the
  procedure title. The Date of Latest Revision identifies the Julian
  date the chart was last revised for any reason. The first two digits
  indicate the year, the last three digits indicate the day of the year
  (001 to 365/6).
  
  The FAA Procedure Amendment Number, located on the left bottom margin
  below the City, State, represents the most current amendment of a
  given procedure. The Procedure Amendment Effective Date represents the
  AIRAC cycle date on which the procedure amendment was incorporated
  into the chart. Updates to the amendment number and effective date
  represent procedural/criteria revisions to the charted procedure,
  e.g., course, fix, altitude, minima, etc.