Which statement is the safest summary?

Cause of Ghayr Munsarif: Additional Alif and Nun

• Every word ending in ان is ghayr munsarif
• Only proper names can contain additional alif-nun
• Additional alif-nun cause منع صرف only under the taught proper-name, adjective, or no-feminine condition; the ending alone is insufficient
• The feminine form never matters