As far as I know, Boker started making the 2020 with Rosewood handles just prior to 1980. They've been making them continuously since then. I searched through the following catalogs:1980, 1982, 1988, 1990, 1993, 1995, 1997, 2001, 2003, 2005, & 2008
All of the 2020 patterns with rosewood handles were listed as having "high carbon steel". They are all shown with the Tree Brand Classic frosted blade etch.
Even the stag handled 2020s (2020HH) after the mid 1980s are listed as having carbon steel blades.
There may be exceptions. Boker may have made some 2020 knives during this time with 440C steel, but it wasn't listed in the catalogs! I hope this helps.
