I am technically not eligible for credit from IL for taxes paid to NY-state because the income was sourced within the state of IL, and I did not physically travel to NY to earn that income. And then IL will not grant a resident credit for taxes paid under the convenience of the employer rule, because it views the income as IL-source and the other state as having an invalid tax claim.
Everyone I know has been filing for the credit anyway and getting it anyway because IL state is not catching it. I spoke to a guy who helped lobby to change some IL tax laws, and he said most tax accountants would actually get this wrong if they filed your taxes because they would also request the credit and chances are it'll go through.
