The earliest machines (1996) have a square front. After that, they started making the front with rounded off corners, but I don't know when.Mine is 1997 and has the square front.
I recently had to replace the brushes in my motor, and there is a date code on motor itself.that may help you if it's the original motor. .mine was 1997, which is exactly what it should have been. If I remember correctly, it is a 4 digit code, starting with a letter..the letters indicate the month.
A January
B February...etc. Mine started with an E, so it was manufactured in May. The next is numerals, mine was "07", meaning it was made in 1997. I already forgot what the fourth letter was for..maybe where it was made? I really don't remember what , or even if I was told anything about the 4th digit, they had what they needed when they got the year, for my purposes of replacing the brushes.
Tin Lizzie's do have serial numbers on them, but as far as I know there isn't a data base for dating them like there is for many other machines.