Chainsaws

I just received a "new" 390XP purchased on Ebay. The Husqvarna box indicated the powerhead should have been SN 20164000385 (so manufactured in the 40th week, 2016) and a PN 965 06 07-01. The unit shipped, however, had a SN of 20150800549 (manufactured in the 8th week, 2015)and a PN 965 06 07-00. The warranty card inside the box had 2016 stamped on it. The unit I received is new, as it has never been used, but it's New Old Stock (NOS) as far as I am concerned.

1. Is the warranty valid for a 2015 unit? When would any warranty expire for the 2015 unit?
2. What issues may be lurking for a NOS 2-year old powerhead versus a newer powerhead?
3. The units have slightly different PNs. What is the difference between the two units?

Thanks