To the beginner, it can be hard to tell an older antique whiskey bottle from a more modern one. One clue is the lip of the bottle, which before 1870  were often roughly made. After 1880, many bottles were lipped using a lipping tool. This gave the bottle opening a more uniform look with less irregularities under close examination.

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After the mid 1920's, machinery was being used to make bottles instead of each one being hand blown by a craftsman. The mold seam goes up and over the lip on antique whiskey bottles made by machines.
If you need more info on antique whiskey bottles, do a quick internet search and you will find lots of resources on different vintage bottles.