Will the new key I'm trying to enter overlap some of the digits in the previously set count value instead of replacing them?
I did say that there was a trap for the unwary and you just fell into it.
Do you have any code saying "I am about to print the number entered by the user so it would be a good idea to clear the previous number from the screen" ?
Answer : no.
Print spaces over the stored number displayed on the LCD before you start printing the new number.