Brother, salam.
You said "mufassir Muqatil b. Sulayman (d. 767). He is reputed to have authored a work titled on the subject which has been reconstructed and edited in his book of tafsir of 500 legal rules relating to the halal and haram".
Have you read the book? May I know where I can find that book? By researcher Goitein do you mean Mr. Shelomo Dov Goitein? Which of his work you are reffering to here? Could you kindly provide a full reference with page number and publisher's information so that we may verify the information for our own research?