1. Your parcel RI939044642CN, we don't know were it's at in USA because I suspect the parcel has arrive in USA. Last tracking is this:
2016-08-20 14:45
Exchange Bureau in Guangzhou, have been exported directly

2. Normally when we see exported directly it mean the parcel in On Route. Now this tracking is confirming that:
International Mail# RI939044642CN Tracking Result
Summary
Tracking number Origin Destination Status
RI939044642CN CHINA UNITED STATES On route

History Detail
Local date/time Activity Location Remarks
18-Aug-2016 18:15 Received by Post Office 52843300
20-Aug-2016 17:46 Departure export customs GUANGZHOU

3. Unfortunately for you, USPS does not track China Post Register Airmail, so we can find out where is the parcel in USA. And Estimate Arrival time for USA can be up to 62 days.

4. I found this for you, but I don't think you will get anywhere but just in case:
http://help.cbp.gov/app/answers/detail/a_id/1208/~/cbp-contact-us-info

5. Also a nice little statement on the FAQ of this forum:

Customs & security delays:
Customs operates on their own schedule, and they don’t care how badly you want your package. Some places open and inspect almost everything, some don’t; some places process packages very efficiently, some do not.

6. for parcel LT086668165CN, this is a tracking that I have found:
Number: LT086668165CN
Package Status: In Transit
Destination Country: United States
2016-08-27 23:59 CHINA, SHANGHAI EMS, Processed Through Facility, Your item has been processed through a facility in SHANGHAI EMS, CHINA at 11:59 pm on August 27, 2016.
2016-08-27 14:59 Origin Post is Preparing Shipment
2016-08-27 14:59 CHINA, Acceptance

Origin Country: China
2016-08-28 01:16 Shanghai City and leave Shanghai to Chicago
2016-08-27 14:59 Shanghai, Cambridge (Headquarters) has been received (the embrace cast member name: Cao Xinhua, Tel: 15801889870)

And this tracking:
International Mail# LT086668165CN Tracking Result
Summary
Tracking number Origin Destination Status
LT086668165CN CHINA UNITED STATES On route

History Detail
Local date/time Activity Location Remarks
27-Aug-2016 14:59 Received by Post Office 201315
27-Aug-2016 23:59 Departure export customs SHANGHAI EMS

7. For this parcel in particular (E Packet), I would advise you to contact the seller as soon as possible to let him know that the parcel has not arrive in USA. He might be able to call China Post to find out what is wrong with the parcel. Unfortunately this week is a National China holiday and not to many person are working including China Post.

8. You are not the first person complaining about a parcel not arriving and all parcels are incoming to Chicago Inbound warehouse. I have read sometime ago about Chicago been the worse place for parcel arrival but did not notice it before a few days ago when people are starting to complaint.

Hope this help.