Which test was it the first time around? I don't know if there's specific medical/scientific data about it yet, but antibodies not being present at all at ~5 weeks and then present in sufficient quantity to qualify for donating plasma at ~7 weeks sounds far-fetched.
First test was Mayo test taken at antibody drive run by Lakewood Bikur Cholim. 2nd test was Mt Sinai test in a Mt Sinai Dr Office.
As far as the results - negative does not mean negative for the Mayo test, it just means its below the 1.01 threshold. The Mt Sinai test which is a different scale had me at 320.
Last - you are looking at dates from onset of symptoms which should not be confused with recovery. You don't start manufacturing antibodies the day that you get sick.
The first test was about a month after I started showing symptoms and unlike the rest of my family, I did not start with mild symptoms. They all had some coughing and then all had loss of taste/smell. The coughing was mild and then the loss of taste and smell hit all 5 of them over the span of 72 hours. Two days later I spiked a fever and had major congestion - which none of them had.
So when my son tested positive for antibodies the same day I tested negative, he was probably a week a head of me in the process.