If the year is over 2050, the new trains can no longer be purchased in the depot. I tried several mods and this seems to be the case. You get the notofication “oh yeah” and the new available vehicles are shown bottom but you can’t buy them.
I did that twice now. I think i havent explained myself well. I can purchase vehicles with the manufaturing date < 2050. Those are still avaialable. If a vehicle has a manufacturing date of 2051 – 2070 (for instance) it doesnt show up in the depot.