Delaware law says a party that has registration membership of at least one-tenth of 1% of the state total is ballot-qualified. The Delaware Green Party registration has increased from 716 members in November 2020, to 749 in March 2021. This increase substantially re-qualifies the party. The requirement is always changing, but currently it is 750 members.
Delaware doesn’t have special elections for legislative vacancies, so it almost never has special elections of any kind, unless it needs to hold a special election for U.S. House, which almost never happens, since it only has one seat. So it is somewhat of a moot point whether a party is qualified during an odd year. However, it is very difficult for a minor party to try to increase its registration in an election year, because for most months of an election year, it is not possible for voters to switch parties. Therefore the Green Party is wise to have done a registration drive during 2021.