Kenko, the point was Mardee was correct, DB months in advance and you proved that by having to go to September to get a discount ticket. But usually MAV has them weeks in advance. Generally 3 weeks in advance, and that can be helpful for those that have to buy closer to the travel date. This isn't a competition, Kenko ... It's a discussion of options.
Like Mardee, I'm one of those who would be happier with all my plans made and bought as early as possible. Mardee has done a lot of travel, smart and one of the best sources here. magtay01 do click on Mardee's name and see the resume. I didn't know if she was aware that MAV, generally not always (so be careful), has discount tickets closer to the travel date than does DB.
Also, and Mardee knows this, all those discount tickets are not refundable or changeable, and the more expensive DB tickets are.
One final note, MAV will sometimes not list a train if they can't sell you a discount ticket. So it's better to start at the DB site to ensure you see all the options, then go to MAV to see if there is a better price.
And the statement that DB opens sales 12 months in advance, might not be totally correct. Apparently its a "depender": Here is a more trusted source for such things: https://www.seat61.com/european-train-booking-horizons.htm which is also a good article in general on when to buy train tickets.
Trains which open 6 months ahead
German Railways international routes: Deutsche Bahn (DB, int.bahn.de) open bookings up to 6 months ahead for most international journeys between Germany and Paris, Amsterdam, Luxembourg, Switzerland, Copenhagen, Prague, Bratislava, Budapest.
When it'll sell a ticket but won't add a seat reservation: For some inwards international journeys, for example Prague to Berlin, you'll find that int.bahn.de will sell you a ticket 6 months ahead, but it can't provide an optional seat reservation to go with it as this has to be sourced from the partner railway's reservation system which still only opens bookings 2 or 3 months ahead. In this case, buy the cheap ticket without a reservation, make an optional seat reservation later if you want one.