COVID-19 was named what it was because it was a new strain of cornavirus discovered in 2019 (dec of 2019 but still 2019).

It got a new name since was a bit different from previous strains of cornavirus.

So, if England and now maybe LA have found new strains that are different from the COVID-19 strain, aren't those COVID-20 and/or COVID-21 depending on exactly when we identified them?

How different does the new strain have to be from the old strain to get it's own new name?