Not sure about Stern coming in later with the LE premium price to follow JJPs higher quality price. The Stern model must have been there earlier than JJPs.
I remember playing my NIB BIBLE more than 12 months before guys were still asking “when is WOZ coming to OZ”.
Stern introduced Premium Limited Editions after JJP started up. I know that well, as JJP started up just as I got into pinball (I thought it died in the 70s, and I squandered the 90s pinball scene by being focused on work!).
JJP announced they were going to do a WOZ just prior to Tron being released, and perhaps even prior to Rolling Stones. Upto that point, Stern had LEs but they were only eye candy improvements to a standard edition. JJP triggered Stern to up spec and up cost their LE playfields, starting with Transformers LE. They later introduced Premium with ACDC's release.