Are you sure the Sobinov 10" Berliner was pressed in Riga? That pressing plant was only opened in September 1902. Can you read "Reproduced in Russia" on backside?
The Recording Angel trademark back is another late feature that seems too late for a 10 inch Berliner.
Here in the UK the only 10 inch Berliners were even rarer and may have only been experimental. Then the equipment went on a recording tour (to Russia among other places). When it returned to London the matrix numbers were about 995 and all recordings after that were all issued with paper labels. But these paper label records had plain backs for quite a while.
I've seen Berliners reissued later with paper labels, but maybe they were earlier types without the embossed lettering, which perhaps they couldn't remove.
Are you sure the Sobinov 10" Berliner was pressed in Riga? That pressing plant was only opened in September 1902. Can you read "Reproduced in Russia" on backside?
”
I have a copy of this record also.. It has the trademarkangel on the back but it has stated "reproduced in HANOVER"