Select all the files at once. Columns align by name — not position — so a renamed or added column doesn't silently corrupt the stack, and the reconciliation report tells you exactly what differed per file.
Copy-pasting files together in a spreadsheet aligns columns by POSITION — one inserted column in March and your whole year is silently shifted. This aligns by name and tells you about every mismatch.
Choose them in one go (Ctrl-click) or add more later. Each file is parsed locally and listed with its row and column counts.
Union mode keeps every column and blank-fills gaps; common-only mode keeps just the columns every file shares. The report shows what was blank-filled or dropped, per file.
Optionally with a _source column saying which file each row came from — then download or open in the dashboard.
The failure mode of manual stacking is silence. This is loud about every mismatch.
A column added, removed or reordered in one file can't shift data into the wrong column.
Per file: row count, columns blank-filled, columns dropped. 'Columns aligned ✓' is something you verify, not hope.
One checkbox tags every row with its origin file — instant month/region grouping in the dashboard afterwards.
All files are parsed and stacked in your browser. Nothing is uploaded.