Panasonic have just replied saying:
Thank you for your e-mail regarding Panasonic Blu-ray discs.
The qualiti of the product has not changed. That the logo is no longer featured was a decision of the Marketing department.
From the information we have there is still a logo “Long term storage” on the box.
“50 Years Archive Life” was a feature that the products can last up to 50 years under optimal conditions.
We can reasure you that the content and quality of the discs have not changed, it was only a redesign of the packaging.
I find this partly reassurring - but I’m still slightly concerned that they may be soft peddling on their previous longevity claims.