--table must have at least 10000 rows, so that it doesn't get lost in NULLs.  I think.
DECLARE @table_name sysname, @date_column sysname, @sql NVARCHAR(4000), @lowest_date VARCHAR(20)
SET @table_name = 'mytablename'
SET @date_column = 'mydatefield'
SET @lowest_date = '20150415'

SELECT @sql = '
DECLARE @tempdate DATETIME, @target_id bigint, @max_id bigint
SELECT @target_id = MAX(id) FROM ' + @table_name + ' with (NOLOCK)
set @max_id = @target_id
SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id

WHILE @tempdate >''' + @lowest_date + '''
BEGIN
	SELECT @target_id = @target_id - 10000000
	SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id
	IF @@ROWCOUNT = 0 SET @tempdate = ''2000/01/01''
END
SELECT @target_id = @target_id + 10000000
SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id

WHILE @tempdate >''' + @lowest_date + '''
BEGIN
	SELECT @target_id = @target_id - 1000000
	SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id
	IF @@ROWCOUNT = 0 SET @tempdate = ''2000/01/01''
END
SELECT @target_id = @target_id + 1000000
SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id

WHILE @tempdate >''' + @lowest_date + '''
BEGIN
	SELECT @target_id = @target_id - 100000
	SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id
	IF @@ROWCOUNT = 0 SET @tempdate = ''2000/01/01''
END
SELECT @target_id = @target_id + 100000
SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id

WHILE @tempdate >''' + @lowest_date + '''
BEGIN
	SELECT @target_id = @target_id - 10000
	SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id
	IF @@ROWCOUNT = 0 SET @tempdate = ''2000/01/01''
END
SELECT @target_id = @target_id + 10000
SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id

WHILE @tempdate >''' + @lowest_date + '''
BEGIN
	SELECT @target_id = @target_id - 1000
	SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id
	IF @@ROWCOUNT = 0 SET @tempdate = ''2000/01/01''
END
SELECT @target_id = @target_id + 1000
SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id

WHILE @tempdate >''' + @lowest_date + '''
BEGIN
	SELECT @target_id = @target_id - 100
	SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id
	IF @@ROWCOUNT = 0 SET @tempdate = ''2000/01/01''
END
SELECT @target_id = @target_id + 100
SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id

WHILE @tempdate >''' + @lowest_date + '''
BEGIN
	SELECT @target_id = @target_id - 10
	SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id
	IF @@ROWCOUNT = 0 SET @tempdate = ''2000/01/01''
END
SELECT @target_id = @target_id + 10
SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id

WHILE @tempdate >''' + @lowest_date + '''
BEGIN
	SELECT @target_id = @target_id - 1
	SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id
	IF @@ROWCOUNT = 0 SET @tempdate = ''2000/01/01''
END

SET @target_id = @target_id + 1
SELECT @tempdate = ' + @date_column + ' FROM ' + @table_name + ' with (NOLOCK) WHERE id = @target_id
SELECT @max_id as max_id, @target_id as lowest_id_for_date, @tempdate as value_for_LowID'

EXEC dbo.sp_executesql @sql