Hello Diego,
As already mentioned by Rupam and Anita, the internal selection logic for identifying such data is quite technical and
cannot be shared . There are several dependencies that are observed to select all the relevant data across different
modules.
However as Thumb rule, we will broadly take care of all such data which falls under a creation/ change /posting etc Dates for the related business process.
For example to identify which all PO /PR / Contract should be transferred for a selected time slice -
We would be checking relevant data from several related tables :
EKKO -
MSEG -
RSEG-
EKBE-
PLPO -
MKPF-
FRET-
EKKN-
Also some dependencies with some PS tables as well.
So for a end user using a system created by TDMS copy , the important thing would be to try testing any business process after the selected 'FROM DATE' . In case any inconsistency is observed for those data, then it should be reported to the TDMS team for root cause analysis. I must add that the overall functional consistency of the data copied by TDMS is already tested in several customer landscapes with no open issues. So you may surely rely on the consistency of data copied by TDMS, of course barring any exceptional cases.
In general you may also go through the note - 1268658 to get an insight of why some extra document may be transferred by TDMS to achieve enhanced consistency.
I hope this answers your query.
Cheers 
Rajesh