@tetrapod, to even want to suggest this would be down to dodgy studbook keeping is rather condescending on the individuals and institution administering the international studbook long term.
As I clearly pointed out previously it is down to the institutions reporting to the studbook holder that may hold the key to not providing accurate data to the studbook holder (but then it would have to be a given that the registrar and curatorial staff at the time of escapes "willingly" did not include these data into their report to the studbook keeper). Without any clear evidence to that effect one cannot concur this, at best it remains a suggestion of how it came to be the escapee data was not included into the studbook.