Select Min Date from CASE statement for date (1 Viewer)

SELECT PURC_ORDER_LINE.PART_ID, PURC_ORDER_LINE.TOTAL_USR_RECD_QTY, PURC_ORDER_LINE.ORDER_QTY, PURCHASE_ORDER.STATUS, 
                  PURCHASE_ORDER.VENDOR_ID, CASE WHEN PURC_LINE_DEL.DESIRED_RECV_DATE IS NOT NULL 
                  THEN PURC_ORDER_LINE.DESIRED_RECV_DATE WHEN PURC_ORDER_LINE.DESIRED_RECV_DATE IS NOT NULL 
                  THEN PURC_ORDER_LINE.DESIRED_RECV_DATE ELSE PURCHASE_ORDER.DESIRED_RECV_DATE END AS NextPoReceiptDate, PURCHASE_ORDER.ID, 
                  PURC_ORDER_LINE.LINE_NO
FROM     PURC_ORDER_LINE INNER JOIN
                  PURCHASE_ORDER ON PURC_ORDER_LINE.PURC_ORDER_ID = PURCHASE_ORDER.ID LEFT OUTER JOIN
                  PURC_LINE_DEL ON PURC_ORDER_LINE.PURC_ORDER_ID = PURC_LINE_DEL.PURC_ORDER_ID AND 
                  PURC_ORDER_LINE.LINE_NO = PURC_LINE_DEL.PURC_ORDER_LINE_NO
WHERE  (PURC_ORDER_LINE.ORDER_QTY > PURC_ORDER_LINE.TOTAL_USR_RECD_QTY) AND (PURCHASE_ORDER.STATUS = 'R') AND 
                  (PURC_ORDER_LINE.PART_ID = 'FIRST ARTICLE')
ORDER BY NextPoReceiptDate DESC

SELECT TOP 1
...
ORDER BY NextPoReceiptDate DESC

-- Define the CTE expression name and column list.
WITH [tools_CTE] ([umetid],
                  [uassetnum])
AS
-- Define the CTE query.
(
    SELECT DISTINCT [met].[id] AS [umetid],
                    [met].[assetnum] AS [uassetnum]
    FROM [dbo].[projects] AS [proj]
    INNER JOIN [dbo].[products] AS [prod] ON [proj].[id] = [prod].[projectid]
    INNER JOIN [dbo].[productpartlink] AS [ppl] ON [prod].[id] = [ppl].[productid]
    INNER JOIN [dbo].[parts] AS [p] ON [ppl].[partid] = [p].[id]
    INNER JOIN [dbo].[partmetoolinglink] AS [metl] ON [p].[id] = [metl].[partid]
    INNER JOIN [dbo].[metooling] AS [met] ON [metl].[metoolingid] = [met].[id]
    WHERE [proj].[id] = @projid
)
-- Define the outer query referencing the CTE name.
SELECT [tools_CTE].[umetid] AS [metid],
       [tr].[tooltypesort],
       [tr].[tooltypetitle],
       [tr].[partnumber],
       [tr].[mettitle],
       [tools_CTE].[uassetnum] AS [assetnum],
       [tr].[toolbudget],
       [tr].[exptoolcost],
       [tr].[toolcost],
       [tr].[toolponumber],
       [tr].[besttoolcost],
       [tr].[toolbudget] - [tr].[besttoolcost] AS [besttoolcostdifference]
FROM [tools_CTE]
OUTER APPLY (
  SELECT TOP 1 [met].[id] AS [metid],
               [met].[tooltypeid],
               [mettt].[sort] AS [tooltypesort],
               [mettt].[title] AS [tooltypetitle],
               [p].[partnumber],
               [met].[title] AS [mettitle],
               [met].[toolbudget],
               [met].[exptoolcost],
               [met].[toolcost],
               [met].[toolponumber],
               CASE
                 WHEN [met].[toolcost] IS NOT NULL THEN [met].[toolcost]
                 WHEN [met].[exptoolcost] IS NOT NULL THEN [met].[exptoolcost]
                 WHEN [met].[toolbudget] IS NOT NULL THEN [met].[toolbudget]
                 ELSE 0
               END AS [besttoolcost]
  FROM [dbo].[projects] AS [proj]
  INNER JOIN [dbo].[products] AS [prod] ON [proj].[id] = [prod].[projectid]
  INNER JOIN [dbo].[productpartlink] AS [ppl] ON [prod].[id] = [ppl].[productid]
  INNER JOIN [dbo].[parts] AS [p] ON [ppl].[partid] = [p].[id]
  INNER JOIN [dbo].[partmetoolinglink] AS [metl] ON [p].[id] = [metl].[partid]
  INNER JOIN [dbo].[metooling] AS [met] ON [metl].[metoolingid] = [met].[id]
  INNER JOIN [dbo].[metoolingtooltype] AS [mettt] ON [met].[tooltypeid] = [mettt].[id]
  WHERE [proj].[id] = @projid
  AND [met].[id] = [tools_CTE].[umetid]
  ORDER BY [p].[partnumber]
) AS [tr]
ORDER BY [tooltypesort],
         [partnumber];

SELECT PURC_ORDER_LINE.PART_ID, PURC_ORDER_LINE.TOTAL_USR_RECD_QTY, PURC_ORDER_LINE.ORDER_QTY, PURCHASE_ORDER.STATUS, 
                  PURCHASE_ORDER.VENDOR_ID, CASE WHEN PURC_LINE_DEL.DESIRED_RECV_DATE IS NOT NULL 
                  THEN PURC_ORDER_LINE.DESIRED_RECV_DATE WHEN PURC_ORDER_LINE.DESIRED_RECV_DATE IS NOT NULL 
                  THEN PURC_ORDER_LINE.DESIRED_RECV_DATE ELSE PURCHASE_ORDER.DESIRED_RECV_DATE END AS NextPoReceiptDate, PURCHASE_ORDER.ID, 
                  PURC_ORDER_LINE.LINE_NO
FROM     PURC_ORDER_LINE INNER JOIN
                  PURCHASE_ORDER ON PURC_ORDER_LINE.PURC_ORDER_ID = PURCHASE_ORDER.ID LEFT OUTER JOIN
                  PURC_LINE_DEL ON PURC_ORDER_LINE.PURC_ORDER_ID = PURC_LINE_DEL.PURC_ORDER_ID AND 
                  PURC_ORDER_LINE.LINE_NO = PURC_LINE_DEL.PURC_ORDER_LINE_NO
WHERE  (PURC_ORDER_LINE.ORDER_QTY > PURC_ORDER_LINE.TOTAL_USR_RECD_QTY) AND (PURCHASE_ORDER.STATUS = 'R') AND 
                  (PURC_ORDER_LINE.PART_ID = 'FIRST ARTICLE') AND (NextPoReceiptDate IN
                      (SELECT MAX(NextPoReceiptDate) AS Expr1
                       FROM      PURC_ORDER_LINE AS PURC_ORDER_LINE_1 INNER JOIN
                                         PURCHASE_ORDER AS PURCHASE_ORDER_1 ON PURC_ORDER_LINE_1.PURC_ORDER_ID = PURCHASE_ORDER_1.ID LEFT OUTER JOIN
                                         PURC_LINE_DEL AS PURC_LINE_DEL_1 ON PURC_ORDER_LINE_1.PURC_ORDER_ID = PURC_LINE_DEL_1.PURC_ORDER_ID AND 
                                         PURC_ORDER_LINE_1.LINE_NO = PURC_LINE_DEL_1.PURC_ORDER_LINE_NO
                       WHERE   (PURC_ORDER_LINE_1.PART_ID = PURC_ORDER_LINE_1.PART_ID)))