Let me put it another way:
Lets say my training update occurs before yours.
You have a player for sale that has played 48 minutes at Center this past week.
But I buy this player from you after my training update has occured BUT before your training update has occured.
Will this player then still have 48 minutes because he has not taken part in any training updates by any team and so his minutes will not be on zero?
Then you get zero training:D Because you miss both trainings... It will show 48 minutes and will get cleared when the next game starts.
Now if I would buy a player from you after you have completed your training, it will show 0 for minutes played this week. Someone could ofcourse test this theory, but I am pretty sure BB-s have thought about people trying to abuse this loophole, that's why they zero the minutes after training.