One of my items on a 1099-B was marked as Box X. The form had the date of sale and proceeds. I calculated the cost basis using my records and the stock was held long term. I entered it in TurboTax but chose Box D or E. After e-filing I was prompted to print and mail in Forms 8453 and 8949 for a different stock sale. I since learned the definition of the different boxes (https://ttlc.intuit.com/questions/3841864-vanguard-1099b-sale-category). Should I amend my return to use box F instead or is it OK as is?
Save your records that show your sale was long term. Since you chose a Long-Term Code, you probably don't need to Amend your return.
If you had entered the original Code X, TurboTax would have asked more questions to try to make the Long or Short term determination.
The IRS has a copy of your 1099-B, and if they want more information or documentation, you have it.
Here's more info on whether to Amend:
Thanks for the information. FYI: TurboTax doesn't give you the option to choose Box X. It only gives you the option to choose Box A - F. The program's help file does talk about Box X but doesn't do a good job in telling you how to choose Box A - F once you do determine if it is a short or long term capital gain.