1. This is the full tracking of your parcels from the China Post EMS site:
LT472942835CN
2016-11-28 00: 00: 00.0 21:55:00 Guangdong Post Express Logistics International Business Sales Department Dongshan Lanwei Station
2016-11-28 00: 00: 00.0 22:54:00 Guangdong Post Express Logistics International Business Sales Department Baiyun Lanwang station to leave the processing center, sent to Guangzhou
2016-11-29 00: 00: 00.0 18:30:00 Guangzhou City to reach the processing center, from Guangdong Province Post Express Logistics International Business Sales Department Dongshan Lan station
2016-11-29 00:00:00.0 18:31:00 Guangzhou City to the Customs and Excise Department
2016-11-29 00:00:00.0 18:32:00 Customs Clearance of Guangzhou Customs Issued
2016-12-11 00: 00: 00.0 01:20:00 Guangzhou City to leave the processing center, sent to USJFKF = ISC NEW YORK NY (USPS)

LT472804136CN
2016-11-30 00: 00: 00.0 23:22:00 Guangdong Post Express Logistics International Business Sales Department Dongshan
2016-11-30 00: 00: 00.0 23:45:00 Guangdong Post Express Logistics International Business Sales Department Baiyun Lanwang station to leave the processing center, sent to Guangzhou
2016-12-01 00: 00: 00.0 18:30:00 Guangzhou City to reach the processing center, from the Guangdong Provincial Post Express Logistics International Business Sales Department Dongshan Lan station
2016-12-01 00:00:00.0 18:31:00 Guangzhou City to the Customs and Excise Department
2016-12-01 00:00:00.0 18:32:00 Customs of Guangzhou Municipality Released
2016-12-10 00: 00: 00.0 15:43:00 Guangzhou City to leave the processing center, sent to USJFKF = ISC NEW YORK NY (USPS)

LT559402515CN
2016-12-12 00: 00: 00.0 20:33:00 Guangdong Post Express Logistics International Business Sales Department Plum Garden
2016-12-12 00: 00: 00.0 21:22:00 Guangzhou City to reach the processing center, from the Guangdong Provincial Post Express Logistics International Business Sales Department Meihuayuan Lan station
2016-12-12 00: 00: 00.0 23:24:00 Guangdong Post Express Logistics International Business Department Baiyun Lanwang station to leave the processing center, sent to Guangzhou
2016-12-16 00: 00: 00.0 08:43:00 Guangzhou City, leaving the processing center, sent to USJFKF
2016-12-22 00: 00: 00.0 10:03:00 Guangzhou City to reach the processing center, from security
2016-12-22 00: 00: 00.0 14:57:00 Guangzhou City to leave the processing center, sent to USJFKF = ISC NEW YORK NY (USPS)

LT527829404CN
2016-12-05 00: 00: 00.0 21:45:00 Guangdong Post Express Logistics International Business Sales Department Dongshan
2016-12-05 00: 00: 00.0 22:39:00 Guangzhou City to reach the processing center, from Guangdong Province Post Express Logistics International Business Sales Department Dongshan Lan station
2016-12-05 00: 00: 00.0 23:06:00 Guangdong Post Express Logistics International Business Sales Department Baiyun Lanwang station to leave the processing center, sent to Guangzhou
2016-12-13 00: 00: 00.0 22:31:00 Guangzhou City to leave the processing center, sent to USJFKF = ISC NEW YORK NY (USPS)
2017-01-03 00: 00: 00.0 00:05:00 Guangzhou City to reach the processing center, from security
2017-01-03 00: 00: 00.0 03:36:00 Guangzhou City, leaving the processing center, sent to USJFKF = ISC NEW YORK NY (USPS)

2. One of the possible cause for delay is this.

3. When your parcel was sent it was not normal condition. Because:

Holiday Season
China Post has too many parcels to send overseas
Not enough room on the Aircraft for parcels
Smog in China/Hong Kong delaying Aircraft or cancelling them
Rescheduling of mail bags
New York overwhelming of parcel incoming from Overseas.

4. Your 2 first parcels (LT472942835CN, LT472804136CN) if your look at the tracking they where held by China Customs for what ever reason.

5. The other 2 parcels (LT559402515CN, LT527829404CN) I don't know if they had a security problem getting on board the Aircraft but came back to the processing center or was it only that no room available or Smog and they came back.

6. Now all parcel are On Route/In Transit from Guangzhou to Hong Kong to USA JFK. If you track the parcel here:
http://www.track-chinapost.com/en

You might better understand what I have describe.

7. I really hope the above parcels gets to your customer in USA. Just continue to track the parcel on the USPS site for any new movement.

Thanks.