False. The spread of printing and the ability to produce multiple copies of sheet music in the middle of the 19th century did not necessarily mean that all copies of chords were printed accurately. While printing technology certainly improved the efficiency of producing music sheets, it did not guarantee that all printed chords were correct.
Mistakes could still occur during the printing process, and the accuracy of the chords depended on the competence of the engraver or typesetter. Additionally, some older or traditional songs might have been transcribed with incorrect chords, especially if they were passed down orally and not widely documented before the advent of printing.
Musicians and composers would often need to verify and correct chords in printed sheet music to ensure accuracy, and the reliance on the skill and attention to detail of the publishers played a significant role in determining the reliability of the printed chords.