That's kind of what I personally interpret the rules to mean. There isn't actually anything in the description about the poison wearing off after a single blow. Notwithstanding that if were only a single strike the much more expensive poison would be dealing half the damage of a simple flask of oil. Will have to wait for more details (hopefully!) on poisons in the DMG.The rule says that poison applied to a weapon lasts for 1 minute. You could rule that each weapon attack during that duration applies the poison. Even with that, its still not that strong a damage upgrade.
Option 1: +1d4 dmg to each hit with that weapon for one minute.
Option 2: victim takes 1d4 damage each round for a minute (maybe a save can end it)
Option3: victim takes 1d4 damage and gains the poisoned condition.
Option 4: +1d4 dmg one time. Need another dose to inflict that damage.
Ask your Dm.
Personally I like Option 2![]()