Hi @Keith_McFarland and welcome to the community!
The solution I tend to use is to rollup your dates via the linked field to your first table with quantities, and add a lookup field to your first table, looking up that most recent date via the linked field. Then add a formula field that checks if the most recent date is equal to the date of the quantity:
IF({Date Rollup (from quantities) (from rolling up)}=Date,“most recent”)
Then go back to table 2 and rollup the quantities conditionally with “where ‘most recent’ contains ‘most recent’” and use the "SUM(values) to add those quantities.
Table 1: quantities

Table 2

Does that helps you?
Hi @Keith_McFarland and welcome to the community!
The solution I tend to use is to rollup your dates via the linked field to your first table with quantities, and add a lookup field to your first table, looking up that most recent date via the linked field. Then add a formula field that checks if the most recent date is equal to the date of the quantity:
IF({Date Rollup (from quantities) (from rolling up)}=Date,“most recent”)
Then go back to table 2 and rollup the quantities conditionally with “where ‘most recent’ contains ‘most recent’” and use the "SUM(values) to add those quantities.
Table 1: quantities

Table 2

Does that helps you?
I missed the step of passing the date back to the original table to perform the match. Brilliant!
Thanks for your help, this solved my issue!