I would disagree with that statement. If you've just passed the LST for a JAA PPL(A), then your licence will be valid for 5 years and your SEP(L) rating for 2 years.
Until you have the licence in your hand and you have signed it, its not valid for anything! If you wish to remain current or gain addituonal experience outside the legal minima, then there is no reason why this should not be deemed as training for the purpose of obtaining or re-validating a licence or rating. If you don't directly use it for that purpose it matters not, the point is you legally can do if you so wish!