Hi Lee and welcome to the forum.
Monarch offers a "verify" process. It checks to see if the painted fields which have been defined as the areas of the report that you want to extract are wide enough to capture the text and/or values that appear in the report.
Basically it prompts you and displays values that seem to be adjacent to the painted field. At which point you may expand the width of the painted field or ignore the prompt.
This is not an automatic process however. You must run the "verify" process manually. You'd click an icon in the toolbar to run it. And while Monarch offers a suite of object based methods and properties for automating Monarch via a COM interface, you cannot automate the verify process.
DataPump allows for automatic verification of field boundaries, and can also trigger messages when the number of rows meeting a certain filter is zero, or under or over a limit. Combining these options with multiple models it's possible to be pretty sure that you've got all the data you need.
One approach is to trap the report in a second model with an empty trap, so selecting every line of every page, then to use a calculated field to determine whether the line should be considered as a valid detail, and to use an external lookup to the table from your main model as a check that you have got the expected data.
With Monarch 10.5 and Excel 2007 or above, you can also use the Monarch Audit feature to export the source report embedded into the Excel table. This won't give you automatic verification, but will make it easier for users to check the source of records.