Just out of interest: do you have to do one nowadays? Doesn't it depend a bit on the discretion of the "energy consultant"?
This can be inferred from the Technical Minimum Requirements for the KfW Program 153
Requirements for the airtightness of the building envelope according to Annex 4 of the Energy Saving Ordinance do not apply as long as no ventilation system is installed and no reduced air exchange is applied in the efficiency house certificate. However, the airtightness of the building envelope of a KfW efficiency house must be determined by measurement. If a mechanical ventilation system is installed, the airtightness of the building envelope according to Annex 4 of the Energy Saving Ordinance must be proven by measurement.
How the condition was in 2012 could at least not be briefly researched on the KfW site. It cannot be ruled out that the blower door test was not mandatory and/or only the execution but not the measurement result was required. This should be clarified with a call to KfW or the energy consultant.
Did you overlook in the discussion that it concerns a building from 2012? Back then there was, of course, still the KfW 70 house. The question is whether a BD test was required under the conditions at that time, and if so, whether a reference value had to be met or only the execution itself had to be documented.