Thank you very much for your reply. It was allkeys.txt that was missing.
I have finally created the classifier that works. I reproduce it here
in hope that it can be useful to someone.
GenericList -sort_leaf_nodes_using dc.Creator -always_bookshelf_last_level
-metadata dc.Creator -partition_type_within_level per_letter
-classify_sections -sort_using_unicode_collation

Thanks again.

Regards

Vladimir