As the name implies, this type of accumulation/cumulation applies between two countries. Bilateral accumulation/cumulation is most common in almost all origin legislations and provides for the use of originating inputs from the partner country of a free trade zone.
It has to be stressed that only originating products or materials can benefit from bilateral accumulation/cumulation (goods which have obtained originating status according to the origin legislation of a given free trade agreement).
In short, this means that input originating in one member country of a preferential trade zone shall be considered as originating input in the other country(ies).
Normally, the originating status of the products or materials has to be documented to the competent authorities with a proof of origin (origin certificate which was submitted when the products or materials had been imported).
Example: A pullover of HS heading 61.10 is manufactured in country A by sewing together knitted fabrics originating in country B. According to the free trade agreement between these two countries, the specific rule of origin for pullover requires manufacturing from yarn in order that origin is conferred to the pullover. The simple manufacturing process of sewing together knitted fabrics in country A would not confer origin and the pullover would have to be considered as non-originating. Nonetheless, the pullover is considered to be originating since it was manufactured with originating fabrics from country B following bilateral cumulation provision in the free trade agreement.