Most forms will only show one record at a time. However, they can show multiple records related to the parent record that the form currently has selected.
Take the Order Entry form for example. I can search and load several order numbers, but only one order is on the form at a time. Since Order lines relate to Order numbers, the form can show multiple OrderDtl records - but only those for the OrderHed selected.
If you want to view multiple Part records in a single form, you should make a dashboard. If you want to be able to edit the fields displayed, it would need to be an updatable dashboard.
Thanks for your suggestions on this. I suspected that what you described was the case but because I’ve seen data managed in a “header-list” fashion in other screens (i.e. security group maintenance for example), I thought maybe it could be done in the Part Entry screen too.