The first 1,000 of these coins did not include a private
key ‘pit’ on the back side, and thus a small ‘bump’ can
be discerned on the hologram surface because the
small round piece of paper containing the private key
is placed directly between the flat metal surface and
sticker. These are popularly known as ‘error coins’.
This ‘structural stress’ has been documented to cause
some damage to the hologram even for those that
are properly stored, such as in the specimen pictured
below (above the ‘L’ and below the first-bits).