I'm not particularly interested in what constitutes a "real astronomical prediction", I'm more interested in the crux of the topic: Are there common traits shared amongst people with similar birthdates that experienced astrologists can identify and use to correctly place an individual into one of 12 buckets based on a short interaction?
I originally was like you and thought the answer was "no, my birthday says nearly nothing about me". However, over the past few years I've made a point to ask all new strangers I meet ("met at a bar" type folks who I had 0 prior connection to, so excluding friends of friends/etc.) who display an interest in astrology to guess my sign and state their astrological confidence. Roughly 85% folks who are "very confident" in their knowledge of astrology correctly guess it first try, often with little to no hesitation (N = ~8). The folks who are not as confident vary: some will also get it first try, some will take a couple, some give up after like 6.
I originally was like you and thought the answer was "no, my birthday says nearly nothing about me". However, over the past few years I've made a point to ask all new strangers I meet ("met at a bar" type folks who I had 0 prior connection to, so excluding friends of friends/etc.) who display an interest in astrology to guess my sign and state their astrological confidence. Roughly 85% folks who are "very confident" in their knowledge of astrology correctly guess it first try, often with little to no hesitation (N = ~8). The folks who are not as confident vary: some will also get it first try, some will take a couple, some give up after like 6.