Views & Filter criteria I've got a filter criteria saying field xyz = NO. Old nodes meeting the criteria above do not get picked up by the filter. When I edit the node, and resave it, only then they appear in the view. Is there a reason for this?
Yes this is possible. You will have to create two or more filter groups which will be separated with an OR condition.

Click "And/Or, Rearrange Filter Criteria" from the drop down menu of the Filters section and then click "Create New Filter Group". After that drag the filters you want in the new filter group and change the condition separating the groups to OR from AND. I would do it as follows:

1st group

Content: Published Yes And

Content: Type = News And

Content: Xyz (xyz) = Yes 

OR

2nd Group

Content: Published Yes And

Content: Type = News And

Content: abc (abc) = Yes