I personally don't think there's any such thing as a Pre-Mattel fake. Mattel moved production to China, which is where the fake dolls are produced. They probably don't have any way to copy the pre-Mattel dolls.

The pre-Mattel's are definately different from the current ones in hair color, hair feel, skin tone, body tags, the thickness of the body, the stamp on their necks. My pre-Mattel Molly and my sis's pre-Mattel Kirsten have a different font used to stamp Pleasant Company on them. They also do not have tags

The odds of your Kirsten being a fake are slim to none, IMO. The factory in China just doesn't have the capabilities to fake a pre-Mattel, again IMO.