Check your players game shape and DMI. If one and / or the other changed, your players definitely have received training.
If they increased a skill you will see a green arrow behind it, a red one behind stamina, if the player lost stamina. Changes in game shape or DMI are never marked.
If you're training three positions with a level 3 trainer you will have to have some patience, because both these factors make training for the single player slower.
If you want to know more about training speed read this:
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