The other suggestion I have is use the system views sys.schemas, sys.tables, sys.columns, sys.types instead of the INFORMATIOIN_SCHEMA views.

I can not recreate the problem you are reporting.  I have run your code, after creating the needed schema, and I do not get any duplicates.

+1000000

Here is my uncommented attempt at this:

create table #TestDates (
  TestDateID int identity(1,1),
  TestDate1 date,
  TestDate2 date
);

with e1(n)...

The only other thing I would ask, is this number going to be seen by the users or are they hidden values used behind the scenes by the system/database only. ...

Thoughts, advice