Ampscript set variable not working

Given that I have already declared my variables... I am trying to set some values to those variables, based on whether a row of data already exists or not...

 VAR @brandID, @Content, @Header, @subscriberkey, @cottage1ID, @cottage2ID, @cottage1Name, @cottage2Name, @viewDate1, @viewedProperties, @viewedPropertyRow, @viewedPropertiesRows, @viewPropertyCount, @viewDate2, @currentDate, @dayDiff,  @bookingRows, @AllBookingRow1, @bookingRowCount, @AllBookingRowCount1, @viewedPropertyID, @AllBookingRow2, @AllBookingRowCount2, @viewedOtherPropertiesRows, @viewedOtherPropertyRow, @viewedOtherProperties, @viewOtherPropertyCount

Could someone explain to me, why this works:

 SET @viewedPropertiesRows = LookupRows("Viewed Properties","Subscriber Key", @subscriberkey, "brandID", @brandID) SET @viewPropertyCount = rowcount(@viewedPropertiesRows)   IF @viewPropertyCount > 0 THEN    SET @viewedPropertyRow = row(@viewedPropertiesRows, 1)    SET @cottage1Name = field(@viewedPropertyRow,"cottage1Name")    SET @cottage2Name = field(@viewedPropertyRow,"cottage2Name")    SET @cottage1ID =  field(@viewedPropertyRow,"cottage1PropertyID")    SET @cottage2ID =  field(@viewedPropertyRow,"cottage2PropertyID")    SET @viewDate1 = FormatDate(field(@viewedPropertyRow,"View1_happenedAt"), 'yyyy-MM-DD')    SET @dayDiff = DateDiff(@viewDate1,@currentDate,"D")   ENDIF IF(EMPTY(@viewPropertyCount) OR @viewPropertyCount == 0) THEN    SET @viewedOtherPropertiesRows = LookupRows("Viewed Properties","Subscriber Key", @subscriberkey, "brandID", 1)    SET @viewOtherPropertyCount = rowcount(@viewedOtherPropertiesRows)    IF @viewOtherPropertyCount > 0 THEN        SET @viewedOtherPropertyRow = row(@viewedOtherPropertiesRows, 1)        SET @cottage1NameOther = field(@viewedOtherPropertyRow,"cottage1Name")        SET @cottage2NameOther = field(@viewedOtherPropertyRow,"cottage2Name")        SET @cottage1IDOther =  field(@viewedOtherPropertyRow,"cottage1PropertyID")        SET @cottage2IDOther =  field(@viewedOtherPropertyRow,"cottage2PropertyID")        SET @viewDate1Other = FormatDate(field(@viewedOtherPropertyRow,"View1_happenedAt"), 'yyyy-MM-DD')        SET @dayDiffOther = DateDiff(@viewDate1Other,@currentDate,"D")    ENDIF  ENDIF

but this doesn't:

    SET @viewedPropertiesRows = LookupRows("Viewed Properties","Subscriber Key", @subscriberkey, "brandID", @brandID)    SET @viewPropertyCount = rowcount(@viewedPropertiesRows)    IF @viewPropertyCount > 0 THEN        SET @viewedPropertyRow = row(@viewedPropertiesRows, 1)        SET @cottage1Name = field(@viewedPropertyRow,"cottage1Name")        SET @cottage2Name = field(@viewedPropertyRow,"cottage2Name")        SET @cottage1ID =  field(@viewedPropertyRow,"cottage1PropertyID")        SET @cottage2ID =  field(@viewedPropertyRow,"cottage2PropertyID")        SET @viewDate1 = FormatDate(field(@viewedPropertyRow,"View1_happenedAt"), 'yyyy-MM-DD')        SET @dayDiff = DateDiff(@viewDate1,@currentDate,"D")    ELSEIF(EMPTY(@viewPropertyCount) OR @viewPropertyCount == 0) THEN        SET @viewedOtherPropertiesRows = LookupRows("Viewed Properties","Subscriber Key", @subscriberkey, "brandID", 1)        SET @viewPropertyCount = rowcount(@viewedPropertiesRows)        IF @viewPropertyCount > 0 THEN            SET @viewedPropertyRow = row(@viewedPropertiesRows, 1)            SET @cottage1Name = field(@viewedPropertyRow,"cottage1Name")            SET @cottage2Name = field(@viewedPropertyRow,"cottage2Name")            SET @cottage1ID =  field(@viewedPropertyRow,"cottage1PropertyID")            SET @cottage2ID =  field(@viewedPropertyRow,"cottage2PropertyID")            SET @viewDate1 = FormatDate(field(@viewedPropertyRow,"View1_happenedAt"), 'yyyy-MM-DD')            SET @dayDiff = DateDiff(@viewDate1,@currentDate,"D")        ENDIF    ENDIF

I feel like I am going crazy, but there must be a rational reason! many thanks