alphabetic interpolation for addresses not working

I’ve noticed several times, that address interpolation for odd/even numbers is working fine, so that any address in between can be found, e.g. Tarpenbekstraße 8, Norderstedt.

But for numbers with alphabetic suffixes it is not working at all: e.g.

  1. Schilfgrund 15c, Norderstedt
  2. Fliederweg 3B, Hamburg

Crosspost, see https://forum.openstreetmap.org/viewtopic.php?id=74626