In languages with a distinction between active (animate) vs. passive (inanimate) nouns, passive nouns don’t distinguish numbers (SG/PL).
Standardized
IF nouns are grammatically distinguished as active (animate) and passive (inanimate), THEN the passive (inanimate) nouns do not show number distinctions.
See #916 for the plurality hierarchy, claimed to hold universally, irrespective of noun class systems.