In the structured date fields, Specify only supports the following 3 options:
Month/Day/Year* (MM/DD/YYYY or DD/MM/YYY), Month/Year (MM/YYYY), Year (YYYY)
Since Specify 7.7, the date format displayed on the form is dependent on your browser’s locale settings. Changing the browser locale would change the date format.
This is based on your region’s date configuration. Starting in Specify 7.8, you can set default user preferences that disable the accessible date picker options and override the browser’s local date configuration.
If you only have a day and year, that would need to go into a verbatim date field in the database rather than the structured date.
If you would like for the date ranges to be structured and searchable by date, they would need to be split into two dates (each in one of the above supported formats). These would be put into separate fields such as startDate andendDate.