Wikibase (or purtle?) assigns blank node ids by just counting up: _:genidN (where N > 0).
Due to how we currently create the Wikidata entity dumps (run 6 dumpers in parallel and finally concatenate their output), we are re-using blank node ids in totally unrelated contexts (as each of these dumpers has their own counter). Does this pose a problem? Do we need to use globally unique identifiers?