I would be willing to guess that a doctor's antibody count may go up for a long time after illness because their profession gives them constant exposure. The same cannot be said for everyone of course, so I would guess that for most people, if they are not regularly re-exposed, their antibody counts will eventually go down. This is normal and expected, but our bodies are designed to remember viruses to which we have been exposed and are able to launch an antibody response if exposed again. Even if reinfected, subsequent infections are usually much milder than the first--if they are symptomatic at all. I would not be surprised if many asymptomatic cases being discovered by current widespread testing are actually second infections happening in people who got sick last winter. There is no way to know this of course, but it's a plausible possibility. Some viruses do get worse with subsequent reinfections, but this is pretty rare and I don't believe it happens with any others in the family of coronaviruses except in isolated cases (there will always be outliers!).