The authors are of the opinion that evidence regarding the complete loss of smell, or anosmia and the loss of taste or dysgeusia in people who had no other symptoms but who tested positive for COVID-19 are mostly anecdotal and therefore should be treated as preliminary and with caution.
Link to article: https://www.cebm.net/covid-19/what-is-the-evidence-for-anosmia-loss-of-smell-as-a-clinical-feature-of-covid-19/