Cross-Sheet Excel Summation Formula

I have an Excel workbook made up of several custom-named sheets. Each sheet holds the same type of numeric data in a consistent cell range, and I need a single formula that will look through every one of those sheets and return a clean total. No macros or Power Query this time—just a robust worksheet formula that I can drop straight into my summary sheet and copy down whenever new sheets are added later.

Key points you’ll need to hit:
• The sheets are not sequentially numbered; their names vary, so the solution has to find them dynamically.
• Only numeric values are relevant—text, blanks, and any potential errors must be ignored.
• The workbook will grow, so the formula should keep working as new sheets are inserted without manual edits.

Deliverable: one tested formula (or a short, clearly explained helper setup if absolutely required) that I can paste into cell A1 of my “Dashboard” sheet and trust it to keep my totals accurate.

Acceptance criteria:
1. Paste-ready formula provided in plain text.
2. Works immediately in Office 365.
3. Ignores non-numeric cells and error values.
4. Continues to work when additional custom-named sheets are added.

Let me know if you need a sample file to confirm your approach; I can share a stripped-down version quickly.