Seems the 2017 software fed RRSP Income into the pension split calculation, also inflated deductions for the age amounts despite correct birth dates result in re-assmt.

In order to match the re-assessment on the amended turbotax return it was necessary to override the automatic RRSP feed into the pension split formula which should apparently only include company pension income, same as the treatment in the 2016 and 2018 software.  This was picked up on re-assessment one year later.