While the deadline to make the Form 1099-SA available to you is January 31, the deadline for the HSA custodian to e-file the form to the IRS is March 31.
If the entire $9,900+ was used for qualified medical expenses, the distribution is not taxable and reporting it properly won't result in any increase in tax liability. However, if you don't amend your tax return to correct Part II of Form 8889, the IRS will not know that the $9,900+ was used for qualified medical expenses and will likely claim that you underreported income. For this reason, it probably makes sense to amend by sending Form 1040-X to show that there is no change in taxable income or tax liability and including the corrected Form 8889. Of course if any portion of the distribution was not used for qualified medical expenses and was not rolled over, that portion of the distribution is taxable and, if you were under age 65 at the time of the distribution, subject to an additional 20% tax.
