ISRCSECT is not the utility to use to get the details of a csect in a dataset. You are not getting definitive answers because it is not a common nor useful utility. I suspect IBM service might ask you to use this utility on rare occasions, but you would not normally use ISRCSECT on your own.
you might run an AMBLIST and see if what you want is among the output.
The answer has been posted a few times already: use the AMBLIST utility. It is the utility to use to get the details of a csect in a dataset
AMBLIST is normally a batch job:
//LIST EXEC PGM=AMBLIST
//SYSPRINT DD SYSOUT=*
//LOADLIB DD DISP=SHR,DSN=MY.MISC.LOAD
//SYSIN DD *
Run it as a batch job to see if it has the information you need. Then, if it has the information you want, from rexx, you should be able to allocate SYSPRINT, LOADLIB, and SYSIN. And invoke AMBLIST through ADDRESS LINKMVS or similar variant.