Help with Calculated Field Logic

I would like your help with the following:

* 3 calculated columns in one table.

* Total Xmas sales last year, Xmas sales up to this week last year, and Xmas sales this year

*Combining all the columns, I get a wrong last year total.

If I comment out this week last year, I get a correct last year total.. I think the problem is with my calculated field logic

IF  (DATEPART('year',[Enquiry Created]) = 2016 AND DATEPART('week',[Enquiry Created]) <= DATEPART('week',today(), 'sunday')+1) THEN '2016 Now'

ELSEIF  DATEPART('year',[Enquiry Created]) = 2017 AND [Event Date] >= ⌗November 1, 2017# AND [Event Date] <= #January 31, 2018# THEN '2017 Now'

ELSEIF  [Event Date] >= #October 1, 2016# AND [Event Date] <= #January 31, 2017# THEN '2016 Total'

ELSE 'NULL'

END

Thanks for your help