Those who were exposed to SARS in 2003 have the antibodies against SARS COVID-19.
A) No they don't, it's a different virus.
B) There are 7,324 in the entire world who are known to have had and survived SARS 2003. That's 0.0000977% of the world's population. It doesn't help the other 99.99991% even if it were true. And it isn't.