If you use the following script, you will flag first and last date of an ID.
Load * Inline
Load *, If(Id<>Peek(Id),True()) as IsFirstDay
Resident TmpData1 Order By Id, Date;
Load *, If(Id<>Peek(Id),True()) as IsLastDay
Resident TmpData2 Order By Id, Date Desc;
Drop Table TmpData1, TmpData2;
With this you can calculate new and removed IDs. The first expression shows new IDs, and the second expression shows the number of disappeared IDs.