Hi RayCanada
What you are seeing are what are called Insert or Replacement notes. They take the place of regular notes that are damaged during production. It used to be that replacement notes were identifiable by a * before the serial number, and later, as an X as the third letter in the serial number. Replacement notes were often highly desired by collectors.
About a decade ago, the X-identifiable replacement notes were discontinued, and other regular appearing notes were "inserted" their places. The Bank of Canada has never released serial number ranges or information about these insert notes. Many
"Brick hunters", or collectors that obtain new sealed bricks of 1,000 notes, would examine them right after opening them, look for anomalous serial numbers in the consecutive runs of numbers, and report their finds to the wider collecting community, as "insert" or "new replacement" notes. Many collectors continue to collect notes from these serial number ranges as bona fide replacement notes, and the Charlton catalogue lists them as such.
Other collectors (myself included) do not trust the process of the reporting of brick hunting finds to the wider community. I personally think the process is open to error and/or abuse and I do not collect them. I stick to collecting older * and X replacement notes, where there can be no question as to their use as genuine replacement notes.
Because this can be a contentious issue, on these forums "new replacement" notes can only be identified as such if they are within the ranges published in certain publications, and a reference is made to which publication this information may be found. More info is in section III of the
CPMF Code of Conduct.
I hope this helps.