Not 100% sure but possibly found a Bug
When going to your farm and training any slave I've noticed that you get the message 'npc name has been trained in vaginal sex.' every single time you trained their pussy. I have yet to encounter a female npc that didn't give me that message on the very first attempt & all subsequent attempts obviously. Not even a virgin will take more than 1 time before getting the completed training message.
I think this is a bug for 2 reasons.
1. Throat & anus training take numerous attempts before getting the message for training completion
2. Most of the times I proceeded with flogging & the rest of training I often got a message stating that the target had been broken but not fully corrupted yet. They would then refuse to sign the slave contract until 1 or more further vaginal training attempts even though the message for training completion would be present every time. (I'd ask them to sign after every attempt until they eventually did)
To put it in perspective, I have trained 11 slaves in my main game so far and noticed this possible issue on slave 3 when she would refuse to sign the contract despite being broken by flogging & being completely trained in all 3 specialties (according to the messages). While uncertain if the message appeared from the very first vaginal training for the first 2 slaves, I know that it has appeared on the first training & all subsequent training for slaves 3 to 11, two of which were virgins.
EDIT
Something is definitely off here. The vaginal training completion message is not always on the first attempt(s) (had 3 more that it took 3-4 times before getting the message out of 6 more trained slaves) however, it is always 2-3 attempts early.