you need to understand that whenever you talk about things that happened before 1950, you need to refer india as indian subcontinent. there was no country india before 1950. present day india was dividied into many kingdom. and same is valid for when you talk about birthday of buddha. buddha was born in indian subcontinent before 2000 CE (common era, scientific term for AD) in indian subcontient (because there was no nepal 2000 year ago) which isa present day lumbini, Nepal.