* Marking diagram from query/list using a date

[donone]

V5
I use both Birth (GRO) and Baptism (Church Record), Marriage (GRO) and Wedding (Church Record), also Death (GRO) and Burial (Church Record) for source entries against individuals. I use flags with icons to mark diagrams to show properly sourced data as opposed to tentative data.
I would like to Mark (colour) boxes in the diagram to indicate at a glance, 'Complete', because looking at flags requires a constant evaluation as to whether all flags must be present to mark complete. They will not necessarily all be present to complete because 1837 says they cannot be.
The evaluation is i.e....
If any of an Individual's B M D are pre 1837 they are not required (available) to cause completion but Baptism, Wedding Burial will be, except with more recent dates where Church Records are difficult/impossible to find but GRO will be available. I will set a date for this.
I am looking to build a query to create a list to mark the diagram.
My difficulty is that I have come to a stop at checking, say, birth/baptism date against 1837 to give a True/False.

Can anybody please suggest how I use the date in the Rows expression.
Failing that is there an alternative.
Thank you.

[tatewise]

I presume the standard Rows filter operators was earlier/later than are unsuitable because you want the true/false result to be part of a larger Expression.

The true/false expression would be something like:
Timespan( DateAt(1837,2,1), %INDI.BIRT.DATE%, DAYS ) < 0

This will be true if DATE is before 1 Feb 1837.
But it will be false if DATE is after 1 Feb 1837 or DATE is not defined.

Change the parameters of DateAt(1837,2,1) for a different date.

However, I would strongly advise you move to using Diagram > Box > Condition > Expressions instead of Record Flags or Marking Boxes. See how_to:using_flags_and_icons_and_expressions|> Using Flags and Icons and Expressions.

Essentially, the same Expression you compose in a Query is used in a Box > Condition > Expression.
The advantage is that you do NOT have to keep running the Query and Marking boxes or adding Record Flags every time you change your data.
The Diagram automatically updates its icons/colours based on the Box > Condition > Expressions.

[donone]

I thank you for that excellent solution. Yes, it was to be part of a possible other expression.
Clearly I needed to have read much more on this. Now probably irrelevant because...
I am grateful for the final advice, which reads to be a very much better solution.
Thanks for the link, I will study that carefully.