The one shot poison is Old School poison, and is a valuable collectible. It was discontinued as is considered rare and desirable by many in-game collectors. DO NOT LET ANYONE FLIM FLAM YOU OUT OF IT.
You can tell the difference because the newer ones are bottled in potion-looking bottles and are good for multiple uses.
seems like the one with the 1/1 is more common, i found some of the OLD tree poison antidotes without the number on them, but it was just a few compared to the rest
I think the technical difference is that, originally, poisons and antidotes never actually had the uses as part of the item name. That was introduced (probably) when the newer poisons and antidotes were introduced with their own n/5. And, as anyone who's experienced changes to items by TS would know, often not all of the old items that already exist update automatically.