I think this should do it:
SELECT tA.ID, tA.[Serial #], tA.[PGI Date], tA.[Close Out]
FROM Table1 AS tA
INNER JOIN Table1 AS tB ON tA.[Serial #] = tB.[Serial #]
WHERE tB.ID <> tA.ID
AND (Abs(DateDiff('m', tB.[PGI Date], tA.[Close Out])) < 4
OR Abs(DateDiff('m', tA.[PGI Date], tB.[Close...