The Monday number I look at first isn't shipments out. It's how Friday's receiving closed.
Here's the actual practice. Every PO that closed last week gets one of two marks: clean, or closed-with-questions. Quantity mismatches, damaged cartons, SKUs that didn't match the packing list, anything that made someone stop and ask. The ratio is the number.
A clean week means this week starts at full speed. A messy week means Monday starts with fires that look like picking problems but aren't. Most ops problems are last week's inputs wearing this week's costume.
If you run your own warehouse, track that ratio for a month. It predicts your week better than your order forecast does.