I thought they can also sometimes identify via last name?

not really, many of the states does not use last name and many take up their fathers name as last name. It also varies from state to state, so the probability of you identifying another person caste from their last name is very small.

With many people taking different names that are modern from parents ,its really hard to know .

My wife has her father's name as her last, so what you say definitely tracks.

You can always ask about someone's background, or look it up.

Google suffered a backlash in Japan when they made ancient maps easy to find, as people feared it'd make it easy to connect them to frowned upon ancestry: https://abcnews.go.com/Technology/story?id=7514420&page=1

You can’t look up this stuff, it’s too local and none of it is written down or relevant even if it was. Just families classifying families in their towns.

> You can always ask about someone's background, or look it up.

Seems easy enough. There are only 4.6 Million possibilities to choose from.

based on the number of subcastes Govt of India identified for a caste census in 2011. https://www.deccanherald.com/content/489752/socio-economic-c...