The Hillsdale cancel is dated the "9" and not the 19th, as first appears.
Consider the following explanation: Postmasters and clerks were very careful with correct dates and were required to make daily impressions in log books. The "9" slug is inserted at a slight angle to the plane of the rest of the cancelation device (red line) in such a manner that the edge of the slug takes ink and makes an impression resembling a "1" before the 9.
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The more interesting error (and a true error), is the Hillsdale device having TWO hour slugs, both 8PM and 2PM instead of the year date slug!