I don't think anyone ever played that way (only counts when it's the highest ball) back when I was getting and giving ball spots at nine ball. If you were giving someone the "7 ball", it was assumed to be good at any time during the game except maybe on the break. If it counted on the break, that could be specified as the "wild 7". If you didn't want it to count on a slop shot, it was the "call 7" and it could be called and made on an early combination. If the call 7 was made by slop by the weaker player, it stayed down and the spot was gone.
A common lesser spot was the "safe 8" which means that if the weaker player makes the 8 at any time, he doesn't win then, but he cannot lose the game. If the stronger player then makes the 9, the game is null. Then there was the "call safe 8" which was nearly a negative spot.
Bottom line: different regions and eras likely have/had different standards and if don't know what the local standard is, you should clarify before the first break.
Which reminds me of a spot I almost gave someone....
Orville played nearly even with me. He also was described by Wayne, the manager of the PH, as having a heart the size of a streptocarpus seed. I don't know how Wayne knew about streptocarpus seed size because he never showed any interest in things botanical, but here are a thousand streptocarpus seeds about to be sown:
View attachment 500543
... smaller than dust.
Anyway, nothing was happening in the PH one evening and I finally get Orville to agree to play some $5 nine ball with him getting the safe 8. We get to the table, flip the coin, he wins and as I go to rack, he says, "I quit."