new
    bool:g_IsFullyConnected[ MAX_PLAYERS char ]
;

public OnPlayerConnect( playerid )
{
    if ( g_IsFullyConnected{ playerid } )
    {
        // do stuff ..
    }
}

public OnPlayerDisconnect( playerid, reason )
{
    g_IsFullyConnected{ playerid } = false;
}

public OnPlayerRequestClass( playerid, classid )
{
    if ( !g_IsFullyConnected{ playerid } )
    {
        g_IsFullyConnected{ playerid } = true;
        
        OnPlayerConnect( playerid );
    }
    
    // do stuff ..
    // don't forget to return 1/0
}

public OnPlayerRequestSpawn( playerid ) // Players that are in class selection during gmx/time out won't request a class upon reconnecting. That's why I use OnPlayerRequestSpawn.
{
    if ( !g_IsFullyConnected{ playerid } )
    {
        g_IsFullyConnected{ playerid } = true;
        
        OnPlayerConnect( playerid );
    }
    
    // do stuff ..
    // don't forget to return 1/0
}