Uwe,
i agree the description for P. bichir bichir and P. bichir lapradei isn't very helpful. It doesn't really point out specific/distinct differences. It's hard tell what the differences are based on just the existing description.
As for Schaefer's Aqualog book, here's my opinion regarding P. bichir bichir. I certainly don't have the credentials like him, but I respectfully disagree with his ID on the LIVE specimens that he showed in the book. I strongly believe those live specimens are what's called 'Guinea lapradei' in the trade. As noted in the book, those specimens were collected in Guinea. As a result, some of his worded description are describing 'Guinea lapradei' and NOT P. bichir bichir.
Personally, the main physical differences I've found between lapradei (from Nigeria) and P. bichir bichir are the typical number of dorsal finlets, and the head shape. There are some pattern differences too, but they can be similar. The description doesn't mention the head shape, but if you see the drawing in the paper Gosse 1990, it clearly shows a difference. And the specimens that have been collected from East Africa (Lake Turkana, Omo River, Nile River), where the holotype was also collected, have shown this difference in head shape compared to lapradei.
Finally, the two also have very different growth rate, and very likely different max size, with the Pbb growing apparently much faster (at least for the ones originated from East Africa).