Tiggerblue10, sorry for the late reply. You've asked a very interesting question with a complex answer.
Fudan university in China conducted an antibody check on 175 patients who had recovered from Covid19 and were effectively asymptomatic. Curiously, they discovered that 10 of those patients had no antibodies present. Right now, no one knows why this was so although 9 out of the ten patients were aged 40 or under. Suggestions have included a fluke in testing procedures, false positives in laboratory PCR results for reasons unknown, contaminated laboratory reagents, poorly trained staff or even the fact that the patients may have had a similar infection to Covid19, such as one of the many atypical pneumonia's. It is also possible that MERS infection was present.
There are other studies with similar and contradictory results that are coming through in academic papers from other parts of the world but nothing is certain. There is also a degree of scepticism over any Chinese research or case studies in recent weeks for varying reasons and I'm afraid the scientific community is fast developing some doubt about information that comes out of the region.
So all in all to answer your question, no one really knows. I've read the original paper but summarised versions are all over the internet if you care to take a look yourself.