> "Has been abolished in 1966" says that it was abolished in 1966 and it remains abolished today.
That meaning would be expressed as "has been abolished since 1966", unless it is still 1966 when the idea is being expressed, in which case "has been abolished in 1966" works instead; "has been abolished" is a present perfect (passive voice) construction so "in <past time period>" doesn't make sense with it, while "since <past time period>" or "in <current time period>" does.
That meaning would be expressed as "has been abolished since 1966", unless it is still 1966 when the idea is being expressed, in which case "has been abolished in 1966" works instead; "has been abolished" is a present perfect (passive voice) construction so "in <past time period>" doesn't make sense with it, while "since <past time period>" or "in <current time period>" does.