Hi MollocH,
It appears that you are using property promotion to get at the first, last etc. But, you could simply do InfoPath import of the previous forms and use the built-in Merge functionality to load the repeating elements. I'm assuming the second form is your report form. That's fine, just add a SharePoint list adapter (for the first form library) and some code to import the forms you want. You could do a dropdown with an import button for the list adapter. Select the form, and click an "import" button that you hook up to code to do the import. Or, you could just have the button load all of the forms.
There is a sample in the InfoPath SDK that describes how to use InfoPath merge/import. In addition, there are two out-of-box solutions that come with InfoPath which have a good example of this: Issue Tracking and Meeting Minutes. The Meeting Minutes form imports the forms from Issue tracking, which includes repeating elements. This is described in chapter 2 of the book as well.
Good luck,
Patrick Halstead [InfoPath MVP]
InfoPathDev
Patrick Halstead
Project Manager at Qdabra