Possible Clues:

• Decade of the Arms crisis, Vietnam and All Kinds of Everything
• Altogether the last three knockout rounds that spanned several years
• It happens, that is to say, in the ship years ago
• In the past then, not, by the sound of them, one over the eight
• Gone past at over six knots, it seems
• By the sound of them, they're not one more than half a dozen a time
• Years ago one sees about the vet in the inside
• Sound as if they're not over six; they're over three score
• Not so 17 across years ago in piggy places
• By the sound of it, not in 9 across some years ago