sql query help

Documents
Docid  Status date

1      abc   12/16/2009
2      CCH   12/22/2009
3      PPD   12/21/2009
 
DocumentsHistory
DochistoryID   Docid   Status   date
   1             1      PPD     12/1/2008
   2             1      GGB     12/13/2008
   3             2      NAF     12/2/2008
   4             2      PPD     12/3/2008
   5             2      Xyz     12/7/2008
   6             3      AAD     12/7/2008



Below query that takes parameters as begin and end date and
I want to get all the records from document history and documents table
 that had  status of PPD atleast once but not the status as XYZ

The query should returns

For above example it will return
 docid status date
  1    PPD       12/1/2008


this will  not get the record docid=2 because it had a status of XYZ in one of the records.
Now I want to change this query so once I get the results from this query, I want to check the next status for that record
(using the datatime in the date field) and if it within the startdate and enddate and then it return the record and there is
no next status (means thats is the latest date of that record with status PPD) it should also get this record. please note that we need to check both the table
So for the above example it should return
For above example it will return
 docid status date
  1    GGB    12/13/2008
  3      PPD   12/21/2009

1:
2:
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Select * from (
Select Docid , Status , date From Documents
union all
Select Docid , Status , date From DocumentsHistory) A
where date berween @startdate and @endDate
and Status='PPD' and
not exists (Select 1 from 
(Select Docid , Status , date From Documents
union all
Select Docid , Status , date From DocumentsHistory) B where 
B.date between @startdate and @endDate
and B.Status='XYZ' and B.DocID = A.DocID)