>>>>Here is a sample:
>>>>
>>>>

>>>>declare @t table (id int identity, col1 Int, col2 Int)
>>>>
>>>>insert into @t (col1, col2) values (1, 3), (2, 5)
>>>>
>>>>select * from @t where not (col1 > 3 and col2 < 6)
>>>>
>>>>select * from @t T where not exists (select * from @t T1 where col1 > 3 and col2 < 6 and T.id = T1.id)
>>>>
>>>>select * from @t where col1 <=3 or col2 >=6

>>>>
>>>>Normally NOT (condition1 and condition2) translates into opposite condition1 OR opposite condition2
>>>
>>>Yes, after second verification, I see that the execution is the same.
>>>
>>>I always use the NOT in such approach as it is more easy to understand. When I have something like this:
>>>
>>>

>>>DECLARE @ModDate DateTime
>>>DECLARE @NoStatus Int
>>>DECLARE @ModDate2 DateTime
>>>DECLARE @NoStatus2 Int
>>>DECLARE @ModDate3 DateTime
>>>DECLARE @NoStatus3 Int
>>>
>>>SET @ModDate='2013-11-09 10:31:18'
>>>SET @NoStatus=5
>>>SET @ModDate2='2014-11-03 10:31:18'
>>>SET @NoStatus2=8
>>>SET @ModDate3='2014-11-03 10:31:18'
>>>SET @NoStatus3=7
>>>
>>>SELECT Client.Numero FROM Client (NOLOCK)
>>> WHERE NOT (Client.ModDate<@ModDate AND Client.NoStatus=@NoStatus) AND
>>>  NOT (Client.ModDate<@ModDate2 AND Client.NoStatus=@NoStatus2) AND
>>>  NOT (Client.ModDate<@ModDate3 AND Client.NoStatus=@NoStatus3)
>>>

>>>
>>>...it seems more easy to understand that the second one:
>>>
>>>

>>>DECLARE @ModDate DateTime
>>>DECLARE @NoStatus Int
>>>DECLARE @ModDate2 DateTime
>>>DECLARE @NoStatus2 Int
>>>DECLARE @ModDate3 DateTime
>>>DECLARE @NoStatus3 Int
>>>
>>>SET @ModDate='2013-11-09 10:31:18'
>>>SET @NoStatus=5
>>>SET @ModDate2='2014-11-03 10:31:18'
>>>SET @NoStatus2=8
>>>SET @ModDate3='2014-11-03 10:31:18'
>>>SET @NoStatus3=7
>>>
>>>SELECT Client.Numero FROM Client (NOLOCK)
>>> WHERE (Client.ModDate>=@ModDate OR Client.NoStatus<>@NoStatus) AND
>>>  (Client.ModDate>=@ModDate2 OR Client.NoStatus<>@NoStatus2) AND
>>>  (Client.ModDate>=@ModDate3 OR Client.NoStatus<>@NoStatus3)
>>>

>>
>>This thing is still very hard to understand for me. I think the easiest here would be
>>
>>and Client.ModDate >=@MinDateOf3Dates OR Client.NoStatus NOT IN (@Status1, @Status2, @Status3)
>
>are you certain that all possible resultsets will be identical with your clause?

Hard to say, but this one I can understand. The above 2 variations are too complex for me.