The Miscellaneous Tariff Bill (MTB) was put into effect on October 13, 2018 and grants duty suspensions and reductions on 1,660 products through December 31, 2020. The MTB provisions are buried in subchapter II to chapter 99 of the Harmonized Tariff Schedule, found here (start searching on page 6). Also note that the tariffs highlighted in yellow have expired, so unless you're looking back at very old entries, those should be ignored.
So what if you're product is now eligible for duty free entry under MTB, but also subject to Section 301 duties from China? With reference to CSMS message 18-000606, CBP recognized that approximately half of the 1,660 MTB-eligible items are produced in China and that there is considerable overlap with Section 301 tariffs. Unfortunately, their position is that while these products can benefit from MTB's duty suspensions and reductions, they remain subject to the 10 or 25 percent tariff imposed by Section 301.
Therefore, you can expect to see a total of three tariff numbers on your 7501 for these lines, they are: (1) the 9902 tariff for the MTB discount, (2) the 9903 tariff for Section 301 duties, and (3) the normal tariff number applicable to the product you're importing.