154. When There’s No Second Torah

24:9 If a disqualifying defect is found in a sefer Torah scroll and no other is available, the requisite number of aliyos should be completed from the defective scroll but without blessings. (If the one in whose aliyah the defect was found has not said his concluding bracha, he should stand at the bimah for the rest of the Torah reading and say the bracha at the very end - Mishnah Brurah 143:29.)

24:10 Some authorities maintain that if a disqualifying defect is found in one book in a sefer Torah scroll, we may still read another book of it. For example, if the error is in Sefer Bereishis (Genesis), we may still read, with blessings, from Sefer Shemos (Exodus). One can rely on this opinion in a pinch when it cannot be corrected or if the error is found on Shabbos or Yom Tov. However, one should not use such a sefer on Shabbos afternoon because that reading is not as imperative; it was originally instituted for the sake of those who cannot attend shul to hear the Monday and Thursday readings.