Perhaps the best way is to refer to your past broker statements that coincide to the same calendar month end historic date you are creating. Note: the historic prices are only required if you are trying to derive IRR performance for such date ranges. If this is not important to you, you can simply start storing historic dates currently, and going forward.
If you have add'l questions, please contact our technical support team directly at techsupport@investmentaccountmanager.com
Matt
