In Mechelen, the 12th and 13th convoy were formed separately. The formation of the 12th convoy was started on 26 September. It could only be completed on 6 October. Of the 1000 people registered, one deportee would escaped before the Belgian border. The other convoy, the 13th, started on October 6, should be completed on 9 October, on the eve of the departure. That is why it only counts 679 people; four of them would jump out of the rolling train before the border.
The two convoys, carrying a total of 1674 people arrived in Auschwitz as one transport on 12 October, after a stop in Kozel. It is also the last time that a "Belgian" convoy stopped here. At this last stop, a max of 356 people were selected as "work-able". In Auschwitz itself, still 28 men were registered too. Only 88 of the 803 deported women and girls were registered. The majority of the 1202 persons who were murdered immediately after arrival were women.
This transport has an eradication number of 71.8% upon arrival. Of the 472 female and male workers in the camps in Upper Silesia and Auschwitz, barely 54 will survive, 28 of the 12th- and 26 of the 13th convoy.
Source: The Memorial of the Deportation of Belgian Jews, page 27.