I was convinced that I had Covid starting 29th February, plus I gave it to our son who got it much worse than me. Many of the symptoms, and I was sure I had caught it during my weekly trips to the pub with my BIL. He was even sicker than me and went to the GP twice in February.
He received a letter from the NHS this week inviting him to take a Covid antibodies test as they are going back and reviewing possible missed cases. They sent him a home test kit, finger prick blood test, take a photo of the result, upload it online and answer a few questions. He did the test last night and got the result today. Negative. Should not be surprised really as his wife (my sister) got it bad enough to be told to go to hospital where she was tested for Covid - negative. She had pleurisy which was amplified by her Lupus.
The problem may be that they're finding that the antibodies may not hang around very long. Hopefully the body's T-cells rememeber the virus longer and will kick up an immune response if the person is exposed again.