Right now there are quite a few 'vintage' F. Herder & Sons folding knives 'showing up' on line. Some have come from the factory collection. Factory closed in 1992. Whomever bought some or all of this collection is now selling some. Or so it seems.
The sod buster style knife shown above has been used, tip is not original, it is rounded off.
Age of these knives cannot be determined because Herder made the same patterns and used the same markings for many decades perhaps even 100 years.
Likely O.P. knives are post WW II but they could be older.
Note: i am far from being an expert in German cutlery. I do collect these knives but do not know any in depth history.
There are ebay sellers with this large ( ~ 4 7/8") F. Herder sod buster asking up to $300. Actual market value is $100 on a good day.