It's ok to take that on faith. If you recover from the virus, it's because your immune system knows how to kill the virus. We don't know of any immune system interactions that don't work that way.
There's a chance that immunity is short-lived, or that there are multiple strains of the virus which do not produce equivalent antibodies, but 100% of scientists will believe you develop immunity of some sort.
Isn't that a case of having multiple strains of the virus, where recovering from one strain still provides immunity to that strain? The gimmick here is that it decreases resistance to the other strain, possibly after some time.
I was hearing some doctors saying on the radio that any flu immunity is short lived, this is why we need to have the anti-flu vaccinations every year, that cover the typical/usual strains. If immunization lasted forever there wouldn't be a need for annual vaccination.
There have been reports, but it’s not to my knowledge clear whether the people who’ve tested positive after being considered recovered were experiencing something else, like a false positive before/after, or weren’t in fact fully recovered.
There's a chance that immunity is short-lived, or that there are multiple strains of the virus which do not produce equivalent antibodies, but 100% of scientists will believe you develop immunity of some sort.