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If Amortization Rule Application (tag 9007) is set to Retrospective, the retro is kicked off with type O (Original Acquisition date) or C (Conversion Date/Settlement Date), based on Retro Start Date.
If the Amortization Rule Application is set to Prospective, a D type retro (Date Specific) is initiated. The earn through date and prior day's LTD amortization numbers are put on the object in the Retro Start Date and the two prior LTD Amortizations (tags 9615 and 9616). In this way, the amortization should pick up prospectively from the Earn Through Date, rather than from the Period Begin Date.
Also, whenever a Run Retrospective Amortization process is run, Eagle Accounting continuously handles amortization retrospectively until the end of the coupon period, so the PTD and LTD amounts are handled properly. After retrospective amortization has run, the rules take the Retrospective Amortization Type (tag 9159) off of the event and put it on the object, along with the Retro Process Date in tag 9614. On subsequent days, the earnings process checks for tag 9614 on the lot, and if it is in the current coupon period, the earnings process activates retro again.
If there is an amortization rule change that only affects some of the lots in a position (because the rule is a lot level override rule), only those lots initiate retro calculations. Earnings accomplishes this by setting the Retrospective Amortization Type to Y for the event on the initial retro calc, so that the rule processes it appropriately, and then sets it back to N before the next lot processes.