There is nothing more you need to do. Your custodian will handle the necessary IRS paperwork.
thank you but my custodian doesn't seem fully informed. They are telling me that they already sent out whatever gets sent out for 2017. I added another $2k to the sep for 2017 but just did that in 2018. They said they made a note that it is to be applied to 2017 . I'm just concerned that if something got to the IRS that said $6k in 2017 contributions, then I'm stating it was really $8k because I added $2k, then there will be a flag or a problem. I know that I will have the documentation to prove it if needed but I would like to avoid having to prove it.
I have had this same discussion with my custodian. The IRS requires them to track the year you put the money in the account - they send you a Form 5498. You are supposed to keep track of the year it is for - you do that by reporting on your return.
Thank you, so they don't actually send the IRS the 5498? We keep track, we report it on the income taxes, etc, and that's it?