This is a replacement note?

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Found this on eBay.  See image below.

The grading company has designated this note a replacement according to the Charlton number (BC-64aA-i).  I want to know how they arrived at that conclusion.  Shouldn't a note like this be replaced and not replacing?

For that matter, if this note is a "set-up" note, what makes it an error?  I guess the fact that it escaped into circulation makes it an error, but otherwise, it was printed deliberately the way it appears. so...

Opinions?

{http://www.give-a-buck.com/special/headscratcher.jpg}

 This was discussed in April  here.

http://www.cdnpapermoney.com/forum/index.php?topic=9399.0

The thread you linked is in the What' It Worth forum.  I'm approaching this discussion from a different perspective than the value of such an item.  The original question remains unanswered: Why has this note been given the designation of a replacement?  What is it replacing?

I would also like to know where does coming from that the note is printed on "thick" paper?  What should be the weight of a note printed on "thin" paper?  It's the first time I see a such designation for 20$ notes...

Besides, the prefix letters "OH" seems to belong to the 5$ serie.  If the (sheet) note was misfed into the press having the set-up for printing the serials of the 5$ notes, it could be a "wrong prefix" note, but does not explain the term "set-up note"...

As far as I know notes weigh 1 gram. So the extra .02 gram doesn't seem like very much to me.

I'm also wondering about the qualification of an extra 0.02 gram on a note to be a "thick paper" printed note...  it's only 2% "heavier" than a "normal" note...So much parameters will modify the weight of a printed note that a variation of 2% is meaningless.

-No paper mill can produce a sheet of paper having a such accuracy in its thickness (2% of variation on a 0,1 mm (0,004 inch) thickness sheet is only 0,002 mm (0,00008 inch), assuming a perfect uniformity, which is not the case).

-The natural moisture in the paper (around 5-10% by weight).  Weighing a paper note on a dry winter day and the same note on a very humid summer day will show a variation more than 0,02 gram in its weight...

-The quantity of the various inks put on the sheet,

-The coating put on the note...

-And in the case of a circulated note, the various amount of dirt and soiling it can accumulate...