Is the date of publication for the edition in hand present on the item
(as opposed to a copyright date for the sound)
If the date given on the piece is before 1971 and there is a (c) by that date, consider that date to be the copyright date
If the date by the (c) is after 1970, that date cannot be the copyright date for the sound.
The industry switched to using (p) for the copyright date of the sound after 1970