Allow a form entry to be a drop-down list with options consisting of those created in column properties in column creation or new entries entered through the form. An example would be a project number, if a line already exists with this project number or if it's a number that was pre-populated as an option during the creation of the column, it appears as a choice and you can select it, if not, you can enter a new one and it then becomes a choice.
We have other sheets with all these project numbers, so using those to create the options for the dropdown list in a new sheet would be even better.
The plan would be to use the above or some other tag to tie data from multiple forms to fill different columns of the same line. Example would be different forms for project requirement questions to be answered by different people. Each has a separate form, but with the same tag (project number) their entries would populate the same row in a sheet.