Between Dates Parameter Query - Extra Records Generated??

Good Evening Everybody,
I am currently helping some people out at work with their database. My knowledge of Access is very limited, and whilst my it is improving I have nonetheless come up against a ‘hurdle’ which I am struggling to jump. The database in question is not complex, quite the opposite in fact. Basically 1 table ‘Main Data’ , 1 data entry form and a few reports. The table includes 8 fields in the following formats:

ID: Auto Number
Area: Text
Equipment:Text
EquipSrlNo:Text
EquipLocalNo:Text
MOPNo:Number
DateDone:Date/Time
MOPPeriodicity:Text


I was recently asked to produce a report for them that would search between two dates using a parameter query and to then return the result. The problem is that when I generate it using the following SQL it returns records in the period that I asked for, but then collects ‘additional records’ which fall outside the date-span that I originally requested, i.e. search Between 03/04/08 And 30/04/08 produces data that relates to data in May, June, July 08 etc. I thought that what I was doing was correct, and it has worked for me in the past- but on this occasion I am absolutely confused???

SQL
SELECT [Main Data].Area, [Main Data].Equipment, [Main Data].EquipLocalNo, [Main Data].MOPNo, [Main Data].DateDone, [Main Data].EquipSrlNo, IIf([MOPPeriodicity]="1",DateAdd("m",1,[DateDone]),IIf([MOPPeriodicity]="3",DateAdd("m",3,[DateDone]),IIf([MOPPeriodicity]="6",DateAdd("m",6,[DateDone]),IIf([MOPPeriodicity]="WEEKLY",DateAdd("ww",1,[DateDone]))))) AS TestDueNext, [Main Data].MOPPeriodicity
FROM [Main Data]
WHERE ((([Main Data].Area)=[Enter Area Type]) AND ((IIf([MOPPeriodicity]="1",DateAdd("m",1,[DateDone]),IIf([MOPPeriodicity]="3",DateAdd("m",3,[DateDone]),IIf([MOPPeriodicity]="6",DateAdd("m",6,[DateDone]),IIf([MOPPeriodicity]="WEEKLY",DateAdd("ww",1,[DateDone])))))) Between [Enter Date Start] And [Enter DateStop]));

Unfortunately, I do not have a copy of the database in question and so I am unable to post it for the purpose of explanation.

Can some kind person point me in the right direction as I am slowly losing the ‘will to live’ Ha? Ha? You have always been so helpful in the past and hence the reason I have called upon my ‘forum friends’ to help me out?


Look forward to your response(s)


Best Regards

CarolW