@Ernst that Sihl plot certainly looks like a convincing match! And the effect of added thickness seems evident there too (in the B measures).
Just before you posted about Babel I was looking at the Aardenberg test pages again for any difference in paper characteristics between print samples that might indicate the paper forumulation changed, but I'm not sure I found anything conclusive. The final print sample (out of 4) shows the white point b* at -0.8, vs the +0.5~0.7 range of the first 3 prints, which seems like quite a shift from blue to yellow. But since that report goes on to describe yellowing that occurs while in storage, and the print seems to have been stored for 8 months before it was measured, it's difficult to infer much about the paper's "true" white point, let alone whether the formulation was changed.
I'd love to try measuring some of my own samples for shifts n grins but I don't have a print spectro, only the screen ones.