A little bird said, "Be careful trying to prove something using dbisql!"

...but I rarely pay attention to little birds, so I missed the fact that dbisql processes each statement (compound or otherwise) as a separate batch.

Watch what happens when dbisql is forced to send all the FOR statements to the server as one batch (which mimics how a stored procedure works with its own BEGIN END block):

BEGIN -- put all the FOR statements inside one block

FOR f_pointless AS c_meaningless INSENSITIVE CURSOR FOR
SELECT row_num AS @row_num FROM RowGenerator WHERE row_num IN ( 1, 2 ) ORDER BY row_num
FOR READ ONLY
DO
   MESSAGE STRING ( 'RowGenerator.row_num = ', @row_num ) TO CONSOLE;
END FOR;

FOR f_pointless AS c_meaningless INSENSITIVE CURSOR FOR
SELECT row_num AS @row_num FROM RowGenerator WHERE row_num IN ( 1, 2 ) ORDER BY row_num
FOR READ ONLY
DO
   MESSAGE STRING ( 'RowGenerator.row_num = ', @row_num ) TO CONSOLE;
END FOR;

FOR f_pointless AS c_meaningless INSENSITIVE CURSOR FOR
SELECT row_num AS @row_num FROM RowGenerator WHERE row_num IN ( 1, 2 ) ORDER BY row_num
FOR READ ONLY
DO
   MESSAGE STRING ( 'RowGenerator.row_num = ', @row_num ) TO CONSOLE;
END FOR;

END;

Could not execute statement.
Item 'c_meaningless' already exists
SQLCODE=-110, ODBC 3 State="42S01"
Line 1, column 1

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So... the cursor-name has to be unique, for no apparent purpose. However, the for-loop-name can be anything; here's a test that works using w, w, w and x, y, z as names:

BEGIN -- put all the FOR statements inside one block

FOR w AS x INSENSITIVE CURSOR FOR
SELECT row_num AS @row_num FROM RowGenerator WHERE row_num IN ( 1, 2 ) ORDER BY row_num
FOR READ ONLY
DO
   MESSAGE STRING ( 'RowGenerator.row_num = ', @row_num ) TO CONSOLE;
END FOR;

FOR w AS y INSENSITIVE CURSOR FOR
SELECT row_num AS @row_num FROM RowGenerator WHERE row_num IN ( 1, 2 ) ORDER BY row_num
FOR READ ONLY
DO
   MESSAGE STRING ( 'RowGenerator.row_num = ', @row_num ) TO CONSOLE;
END FOR;

FOR w AS z INSENSITIVE CURSOR FOR
SELECT row_num AS @row_num FROM RowGenerator WHERE row_num IN ( 1, 2 ) ORDER BY row_num
FOR READ ONLY
DO
   MESSAGE STRING ( 'RowGenerator.row_num = ', @row_num ) TO CONSOLE;
END FOR;

END;

RowGenerator.row_num = 1
RowGenerator.row_num = 2
RowGenerator.row_num = 1
RowGenerator.row_num = 2
RowGenerator.row_num = 1
RowGenerator.row_num = 2

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No, I don't go looking for trouble... I stepped on that SQLCODE -110 in a real stored procedure with a whole series of FOR loops... sassenfrassenfrickenfracken! :)