I've just tried to replicate this booking for you (using the German version of bahn.de).

The system came up with two fares, the "summer special" fare of EUR 29 per person and the normal fare which was well over EUR 100.

When I selected the "summer special" fare it told me there was no availability - so the "summer special" contingent must have sold out.

When I selected the regular fare it told me that availability would have to be checked manually, and took me to a "request availability" screen. I didn't take things any further.