12.18. Use of shipping manifests, bills of landing and other transport documents. It is good practice to use such documents for verification purposes or when customs declarations are absent. However, it is recognized that such practice should be limited, owing to resource constraints and other considerations, to important and exceptional cases.
12.19. Time of recording in enterprise surveys. Countries applying the general trade system frequently have to use enterprise surveys to ensure complete coverage of their trade statistics. The date of exports or imports indicated in such surveys reflects business accounting practices, and, normally, will not coincide with the date of lodgement of the corresponding customs declaration or with the time of physical crossing of the country’s border, but rather with the time when goods change ownership.
12.20. Use of time of change of ownership. In exceptional cases where the general guideline of recording goods when they enter or leave the economic territory is not applicable or is insufficient (for example, in the case of trade in ships and aircraft), IMTS 2010 (para. 1.4) recommends using the criterion of change of ownership to determine whether certain goods should be recorded. In such cases, the time of recording should be determined by the time of change of economic ownership. The time of change of ownership is defined in accordance with 2008 SNA and BPM6 as the time of change of economic ownership from a resident unit to a non-resident unit. The time when the economic ownership changes from a resident unit to a non-resident unit can be approximated by the time when claims and obligations arise, are transformed or are cancelled. Although the principle is clear, its implementation is far from simple, as parties do not always apply the same rules. Even when they do, differences in actual recording may occur for practical reasons such as delays in communication. Consequently, transactions may be recorded at different times by the transactors involved, sometimes even in different accounting periods. It is therefore good practice for trade statisticians to consult with compilers of balance of payments and national accounts as necessary.
12.21. Time of recording of trade over fixed transmission lines. Trade in goods which continuously cross borders over fixed transmission lines (e.g., pipelines for the transmission of oil, natural gas or water, power lines for the transmission of electricity, etc.) should be allocated to the proper shortest reference period based on (a) the actual period of transmission recorded in the customs declarations submitted by the line operators or (b) their administrative records, following the same requirements as for all other enterprise surveys conducted for the purposes of compilation of trade statistics. It is good practice for compilers of the exporting and importing countries of such goods to agree on the compilation procedures, including time of recording, in order to ensure data comparability.
 International Monetary Fund, Balance of Payments and International Investment Position Manual, 6th ed. (Washington,D.C.; 2009).