According to the server style guidelines,

Use camelCase for most varNames. Use ProperCase for names of classes and structs. Use camelCase for instances of such classes.

However, at least three other classes exist with the name Date.

src/mongo/db/exec/document_value/document_value_test.cpp:1155:class Date {
src/mongo/db/pipeline/expression_test.cpp:441:class Date : public SingleOperandBase {
src/mongo/db/query/datetime/date_time_support.cpp:642:struct Date { 

These entities should be unified under clear new names.