Ok ... first the superceeded return (that had to be mailed in) takes months to process and since it is so rare for a personal return to be superceeded (since amending is the most common way to change a return) it is very possible that the data input operator at the IRS simply thought it was a duplicate return and put it in the trash. And an amended return can be filed anytime after the original return was filed although it is best to wait for the original return to be fully processed first. So you did not have to wait until July to amend the return. At this late date, since you are talking about a 2019 return, I highly suggest you check the return transcript to see what the IRS has on file for you and if the "superceeded" return has not been registered yet then file the proper amendment instead now.
