Dialog - how to stop user clicking Next if invalid serial no

[get101]

In a dialog form, I added a new edit control for the user to enter a serial number.

The Next button should only be able to be clicked when a valid serial number is entered.

So I created these rules:

IF (edtSerial.Text = "BB9132") THEN Next.Enabled := True
IF (edtSerial.Text = "TT7345") THEN Next.Enabled := True
etc (20 lines in all)

The Enabled property of the Next button was set to False.

When I ran the Test dialog the Enabled button never turned to Enabled.

Am I doing this correctly?