I'm using cfspreadsheet to create an xls report. One of the sheets (xls tabs) has a summary report which will display some values from different sheets. I see that there is a function to get cell values - SpreadsheetGetCellValue(spreadsheetObj, row, column) - this seems to only get values from cells on the same sheet.
No, you're not overlooking anything. You can interact only with whichever sheet is 'active', at any given time.
If you know the name of the tab, or the position index of the tab, and which cells have what information you seek, you can set that tab as active, get the information and save to variables, then switch to whatever tab you want and continue.