You need to wait for the first amendment has been PROCESSED by the IRS not just accepted for processing. Only then should you file the second amended return AND you will have to mail it in.
note that the time it will take the IRS to process the second amendment and mail a refund is not known for certain. It could take 6 months or more since it is severely behind in processing mailed returns.
The amendment is for a corrected 1099-DIV that I received, which is just a few tens of dollars different from the original, and the tax impact is also just $20+ or so (that I have to pay). Any idea if I just simply skip paying this and if the IRS wants to send me a notice to pay later, I will do so (perhaps including some interest due etc.). This could potentially save me the effort to print out tens and tens of pages to mail this return manually, since it looks like efile is not an option for an amendment of an amended return. Any downsides to not doing this at all?
In fact, I had read somewhere that you can efile three times, which I why I attempted. [FYI, my original return was filed on time, and the first amended return was filed in early June. In both cases I owed money which I sent via ACH and confirmed it was withdrawn. In both cases, I got a notice that the return was accepted. I don't have a way to tell if the return was "processed", and wonder if TT can figure this out even].
I do not know what "starting in a proper manner" exactly is. But, this is what I did: After opening TT, I clicked on Amend a return, and then picked the previously amended return file to start/amend from (as this had the latest changes). Then simply went through the step by step for the relatively minor changes to my 1099-DIV till I got stumped. See any issue with this?
to file a 1040-X you don't need tens and tens of pages.
Include any new/corrected tax document only if it shows federal tax withheld, and include in order only those Sequence Numbered IRS forms and Schedules that changed or were added due to your amendment.
Do not include your old 1040 nor your revised 1040 because the Form 1040-X reflects any changes there and becomes your new tax return.