Standard posters are 25cm x 70cm and exist with four different motives. To prepare them for a specific concert a sticker with the respective information is printed and put on the poster. Printing the posters in 50cmx70cm is really cheap (they are black and white - i.e. only "one color") if you order around 1000 copies. Cutting is for free, so essentially per concert the stickers are more expensive than the posters. Still a very reasonable way to get cheap posters in a decent and unusual size.
Non-standard posters (in Din A3) are produced whenever I feel like making one. Note that "...plays Elgar" is culled from a web-flyer since the poster itself was in portrait orientation. This was USO's March 2013 concert.
The May 2020 concert got cancelled due to corona virus pandemic restrictions. The program got rescheduled for 2020 and 2021.
The same happened to February 2021, unfortunately. The program got rescheduled to May 2021.
May 2021, still Corona, stil restrictions. No reheasals and, consequently, no concert. The program got rescheduled to 2022. Hopefully.