While lack of records may complicate the determination of the amount of loss carryover that remains available to be reported on tax returns for years that are still open, it does not change the necessary process for doing so. For each closed tax year (2008-2011) the amount of loss that *should have been* reported must be calculated and reduces the amount that remains available to be reported on the amendment for 2012 and beyond.
It seems that your concern might be that the loss carryover would be mysteriously (to the IRS) appearing on the amended tax returns without having been present on the 2008-2011 tax returns and that this might raise a red flags with this IRS. However, this is addressed with properly prepared explanation statements included with the amendments. These explanations should show the amount of loss carried over from 2007 and the reductions from that amount attributable to the applicable loss determined from each of the recalculated tax returns leading up to the tax return being amended. If the IRS finds that explanations insufficient, the IRS might ask to see amended 2008-2011 tax returns to substantiate the numbers in the explanations, but amendments for 2008-2011 would not result in any tax refunds for those years.
