How Same Lot Selection Affects
TradeProcessing
When you use same lot selection, you identify an accounting basis within an entity as the controlling basis for lot selection. When the system executes a trade on both bases, it uses the lot selection results of the controlling basis to perform lot selection for the non-controlling basis.
The original event id (tag 457) acts as a common lot identifier and the common link across lots for multiple accounting bases. This identifier indicates that a lot in a position on one basis is the same lot on another basis. Due to fractured lots caused by wash sales, multiple lots on one basis can correspond to a single lot on another basis. This tag has the same value on the fractured lot and its sub-lots in the case of wash sales and should be true for converted lots across bases. With conversion lots, you must load the same value for tag 457 on each lot that is considered the same across bases.
About Automated and Manual Same Lot Selection
TEXT
As part of this enhancement, the Original Event ID field (tag 457) has been established for all wash sale fractured lots and sub-lots, and the identified lot (IDLOT) selection method has been changed to relieve multiple lots based on the same Original Event ID. This resolves the difficulties with present wash sale processing, during which an open could fracture a lot to allow for the disallowance of a prior loss, and the same lots could not be closed across the multiple accounting bases for the entity. The Conversion and Receive trade panels were also revised to allow the submission of the Original Event ID field (tag 457) to identify the same lots across multiple accounting bases.