This should help.
http://www.ibac.org/Files/CNSATM/Library/MNPSA_2008.pdf
You are correct in stating The OTS routes change from day to day to take into account of meteorological conditions (including VA) and tha PTS routes are fixed. But even the flexible OTS have common portions which are generally fixed and there is also the 'Blue Spruce Routes" which are also fixed and for aircraft which can't meet the Minimum Navigation Performance Specifications (MNPS). The manual should explain all.
The SST routes are a bit redundant since the last supersonic airliner had been retired!