i note the spec says (p154):

Description:
The DateTime type represents date and time values with potential uncertainty within CQL.
CQL supports date and time values in the range @0001-01-01T00:00:00.0 to @9999-12-
31T23:59:59.999 with a 1 millisecond step size.

however there there is a test case defined which suggest this should throw:

define Predecessor_min_date: predecessor of DateTime(1900,01,01,0,0,0,0)

https://github.com/cqframework/clinical_quality_language/blob/master/Src/coffeescript/cql-execution/test/elm/arithmetic/test.coffee#L344