The pound has tended to rally whenever Brexit has seemed to be softening, or delayed or even not happening at all. Conversely, the pound has been sold on any sign that a no deal, or generally disorderly Brexit is the more likely.
The ECCN is the Export Control Classification Number. This code represents the classification of an item in the EAR Commerce Control List (CCL) which identifies the items that are controlled by the EAR. The five-digit alpha-numeric designation represents the Category (numeric), Product Group (alphabetic), and Type of Control (numeric). An example would be 9A991, identifying the Aerospace category, the End-Item product group (A), and the Anti-Terrorism / Crime Control / Regional Stability reason for control .
An ECCN is normally provided by the manufacturer of an item. It can be self-determined by the company or, if assistance is needed, a request can be made to the Department of Commerce, Bureau of Industry and Security (BIS), for which you will obtain a CCATS (Commodity Classification Automated Tracking System) document.
Duty recovery is receiving back duty or fees from CBP that were overpaid. Common ways for duty to be overpaid is by not claiming a Free Trade Agreement at the time of entry, using an incorrect classification or value, or re-exporting imported goods after processing.