Thank you, that's useful information, and it tells me one thing immediately.
The three tanks listed as Bef.Wg. are the ones clearly photographed in the "507 44" gallery, named A, B and C.
Knowing their serial numbers, we can see that the 20-ton jack was provided on Tigers as early as 250734.
But, in the book "DW to Tiger 1", Doyle and Jentz assume that this jack was present only from 250772.
If you read their description in 188.8.131.52, they say the mount on the hull was modified at this time, to support the heavier tool.
I wonder if there's a simple explanation; that the tool itself was introduced before the mount was upgraded to hold it? This lack of synchronisation is typical of Tiger modifications.
Tiger research tweets