TEST STEPS:

1- Create basic workbook /tmp/updtest.xls containing just sheet "Sheet1"
   XLSGEN INPSTMF('/hssfcgi/examples/XLSUPD/updtest_Sheet1_create.txt')
          OUTSTMF('/tmp/updtest.xls')   

2- Add sheet "Sheet2" to workbook /tmp/updtest.xls
   XLSGEN INPSTMF('/hssfcgi/examples/XLSUPD/updtest_Sheet2_addto.txt')
          OUTSTMF('/tmp/updtest.xls') ADDTO(*YES)

3- Download workbook /tmp/updtest.xls to your PC, and look at it:
   "Sheet1" cell B2 displays value  "1"
            cell B3 displays value  "2"
            cell D5 displays value  "3" from formula SUM(B2:B3)
   "Sheet2" cell B2 displays value "10"
            cell B3 displays value  "5"
            cell D5 displays value  "3" from formula Sheet1!SUM(B2:B3)
            cell D6 displays value "15" from formula SUM(B2:B3)
            cell D7 displays value "18" from formula SUM(D5:D6)

4- On your PC, change Sheet1 cell B3 value from "2" to "35"
   Excel re-computes the formulas and 
   "Sheet1" cell D5 displays value "36" from formula SUM(B2:B3)
   "Sheet2" cell D5 displays value "36" from formula Sheet1!SUM(B2:B3)
            cell D6 displays value "15" from formula SUM(B2:B3)
            cell D7 displays value "51" from formula SUM(D5:D6)
   Save this workbook and exit Excel.

5- Upload workbook /tmp/updtest.xls from your PC to IBMi

6- Change Sheet1 cell B2 value from 1 to 21 by running command 
   XLSUPD WRKBOOKIN('/tmp/updtest.xls') WRKBOOKOUT(*SAME) SHEETIN(Sheet1)
          INPSTMF('/hssfcgi/examples/XLSUPD/updtest_Sheet1_upd1.txt')

7- Download workbook /tmp/updtest.xls to your PC, and look at it.
   Formulas directly or indirectyle referencing Sheet1 cell B2 do not show the new correct results: 
   "Sheet1" cell D5 still displays value "36" (instead of "56") from formula SUM(B2:B3)
   "Sheet2" cell D5 still displays value "36" (instead of "56") from formula Sheet1!SUM(B2:B3)
            cell D7 dstill isplays value "51" (instead of "71") from formula SUM(D5:D6)
   
8- However, if you go back to IBMi and refresh formulas in workbook /tmp/updtest.xls with command
   REFRESHF WORKBOOK('/tmp/updtest.xls')
   when you download workbook /tmp/updtest.xls to your PC 
   formulas directly or indirectyle referencing Sheet1 cell B2 now shope the new correct results: 
   "Sheet1" cell D5 displays value "56" from formula SUM(B2:B3)
   "Sheet2" cell D5 displays value "56" from formula Sheet1!SUM(B2:B3)
            cell D7 displays value "71" from formula SUM(D5:D6)