So am I correct in thinking that you cannot read what has been sent in the serial monitor because when you print the result that is then put in the serial buffer and send with the next load of data, therefor you used the LED for verification instead?
You can use a serial port to talk to ONE other device - either the Serial Monitor application OR the Arduino (as you are doing). Not both.
So, yes, that is why the LED was used, instead of trying to use the Serial Monitor.