If I understand you correctly - you already have:
1) Summary of # of Meeting Minute Items (related to the Meeting Minute)
2) Lookup to the summary field - call it [Current # of Meeting Minute Items]
My suggestion would be:
- Create a Formula Numeric field called [Next Item Number]- in the Meeting Minute Item table.
Formula would be:
[Current # of Meeting Minute Items} + 1
e.g. If you have [Current # of Meeting Minute Items] is 6, then [Next Item Number] would be 7
So say you have a Numeric [Item Number] field in your Meeting Minute Item table.
Then in your form rule - you can say:
If [Item Number] is blank
change [Item Number] to the value in the field [Next Item Number]
And uncheck the box that says "Fire "change" actions only when a condition changes from false to trueonly change this when this becomes true".
Then this form rule would always apply when the [Item Number] is blank.
This will work as long as you're only adding Meeting Minute Items, and not deleting items in the middle, etc. But you can always Grid Edit the Meeting Minute Items and update the [Item Number] if you need to re-order the items.
Let me know if this helps.