A legal position is any position reachable from the starting position by a valid game of chess, i.e. a sequence of legal moves. Thus there are no such position

A legal position is any position reachable from the starting position by a valid game of chess, i.e. a sequence of legal moves. Thus there are no such positions. Every legal position can be arrived at by playing a legal move from another legal position. That includes the starting position, since Nf3 Nf6 Ng1 Ng8 cycles back to it.