As far as I'm aware - and I've had a look at some of them - most of the German Lawn Tennis Handbooks/Annuals don't include the results even from tournament finals, just the names of the winners and runners-up. A couple of years ago I was able to go through all of "Der Lawn-Tennis-Sport" and "Lawn-Tennis und Golf" up to 1915, so got a lot of results and information from them. The period 1919-27 really needs a good look at where tennis in Central Europe is concerned.
the annual that i have shows all german tournaments for 1908 and the respective winners and number of participants. sadly without results