Mintage discrepancy

Sometimes coins have a very specific odd mintage number - for example:

N#60693

I guess the original intended mintage was 20.000 pieces - now it says actual mintage 5,572.

What is the reason for this and how can we know this specific number?

The coins were not made “on demand” I guess - so they originally made 20.000? Then they couldn't sell it and the were melted?

I hope someone can give me a little insight here. :)

Mints will normally have an issue limit that they sell up to. Not all are sold so the figures you see are final minted figures. Some mints will mint in batches on demand others melt down just depends 

The royal mint did exactly the same with the 2009 blue Peter athletics fifty pence they sold just under 20,000 as they were not meant for circulation, and melted the rest down 

According to our guidelines, the mintage is the number of coins struck.

In the case where 20,000 were authorized but 5,572 were struck, our mintage should say 5,572.

In the case where 20,000 were struck and 14,428 were melted, our mintage should say 20,000 and the comment should say something like "14,428 melted at mint." 

KM has the mintage listed as 5,572.