Because a date transformation step is included in the fallback template (see T308354 for a discussion of whether this should continue to be the case), partial dates returned by Citoid, some of which may be incompatible with English Wikipedia's citation templates (see T132308), are (incorrectly) force-coverted to full dates. For example, 2020-12 is converted to 2020-12-01, and 2020 is converted to 2020-01-01.

Alternatively, change documentation to reflect that only "YYYY-MM-DD" are supported.