Comparing year over year data

Bad data, bad data types, and bad formatting aside, if you're getting a month of data for present and previous year, you don't need to have four variables; one will do. But it should be a date, not a string. I also recommend avoiding BETWEEN since it only works in an extremely narrow set of circumstances.

DECLARE @startdate date = '20170101';

DECLARE @HoldingPattern TABLE
(
  salesman varchar(100),
  saledate date
);

-- let's ignore the illogical dates
INSERT @HoldingPattern (salesman, saledate) VALUES
 ('BOB', '20170123'),('BOB', '20170130'),('BOB', '20170124'),
 ('BOB', '20170130'),('BOB', '20170130'),('BOB', '20170130'),
 /*('BOB', '20170230'),*/('BOB', '20170227'),('BOB', '20170331'),
 ('BOB', '20170327'),('BOB', '20160123'),('BOB', '20160130'),
 ('BOB', '20160124'),('BOB', '20160130'),('BOB', '20160330'),
 ('BOB', '20160330'),('BOB', '20160330'),('BOB', '20160227'),
 /*('BOB', '20160231'),*/('BOB', '20160227');

SELECT
  Salesman,
  [2017 Data] = COUNT(CASE WHEN saledate >= @startdate 
    AND saledate < DATEADD(MONTH, 1, @startdate) THEN 1 END),
  [2016 Data] = COUNT(CASE WHEN saledate >= DATEADD(YEAR, -1, @startdate) 
    AND saledate < DATEADD(YEAR, -1, DATEADD(MONTH, 1, @startdate)) THEN 1 END)
FROM @HoldingPattern
GROUP BY Salesman;

Result:

Salesman    2017 Data    2016 Data
--------    ---------    ---------
BOB         6            4

Further reading:

• #BackToBasics : Dating Responsibly
• Bad habits to kick : mis-handling date / range queries
• Bad Habits to Kick : Using shorthand with date/time operations
• What do BETWEEN and the devil have in common?