Clough and Cummings were not infallible and their spelling may be derived from a secondary source, they did not have access to complete French and German catalogues either as I understand it, they however tried to put everything of serious worth into WERM though.
They were fairly thorough in tabulating lieder, although with such a popular song as the Grieg they didn't bother listing every copy and reverted to 'etc,etc.' and so Steiner does not show up. They also have him as a tenor rather than a bass.
When EMI was formed, including Pathé in March 1931 it is possible that due to the ongoing financial difficulties in keeping the business on the road these records may never have been issued, although they may have been advertise in advance and this is the source. Maybe this is why no one has seen them or heard them.
The works as listed appears to have been recorded in German [again a presumption]- maybe Steiner was German and the French advert just used thew local lingo, maybe the records were for the German market - who knows!
Problem is there are too many variables at the moment and unless more info turns up its difficult to be exact. The important thing from all this is that Rudolf Steiner the Philosopher, who died in 1925, did not make these recordings.