I recently rediscovered in my files several photocopied sheets of chords similar to the one below. A friend (deceased in 2014) gave them to me many years ago.
There are a total of 11, covering keys from D♭ (5 flats) to B (5 sharps). I'm not sure if G♭/F♯ was an intentional omission or just missing from the set I received.
Anyway, I never really used them as I preferred to think in a more key-independent way (e.g. with roman numerals rather than enumerating everything for every key). The chord substitutions are not terribly surprising for mid-20th century popular songs, but I wonder whether anyone recognizes the charts as part of a particular course or system. It could also be that they were just sold as a set on their own.
