Is PART a valid PLI program variable?
('TBCREATE', 'INVNT701',' ', PART, 'NOWRITE', 'REPLACE');
TBCREATE is expecting the names of the table columns. But since 'PART' is not quoted, the compiler will provide the value of the PART variable. ISPLINK will never see that you wrote PART as part of the call.
If PART= 'PART', then you will get what you want, but if it is not, then you get the results you are seeing.
And that is why we ask for the details of all of the calls.