GPT-5.5 vs GPT-5.6 Solfor spreadsheets & Excel

Faults:

1. **`VLOOKUP` column index is invalid**  
   `Sheet2!A:D` has only **4 columns**, so `VLOOKUP(...,5,...)` is impossible. The largest valid column index is `4`.

2. **The date criterion should be parenthesized for clarity**  
   Use `">" & (TODAY()-30)`.

Corrected formula:

```excel
=SUMIF(A:A,">"&(TODAY()-30),B:B)+VLOOKUP(C1,Sheet2!A:D,4,FALSE)
```

If you truly need the 5th column, then the lookup range would have to include column E, e.g. `Sheet2!A:E`, but you said Sheet2 only has columns A to D, so `4` is the correct maximum colum…

**Fault:** `VLOOKUP` requests column **5**, but `Sheet2!A:D` contains only **4 columns**. This normally produces `#REF!`, not `#VALUE!`.

Assuming the intended return column is **D**, use:

```excel
=SUMIF(A:A,">"&(TODAY()-30),B:B)+VLOOKUP(C1,Sheet2!A:D,4,FALSE)
```

The original `SUMIF` criterion is valid; the added parentheses simply make the date calculation explicit. If a fifth return column is actually required, the lookup range must extend to column E instead:

```excel
=SUMIF(A:A,">"&(TODAY()-30),B:B)+VLOOKUP(C1,Sheet2!A:E,5,FALSE)
```