I've studied Polycarp, though never in great detail, yet my hunch is that this film is probably quite accurate as a docufiction. I think that it was well acted, insightful of the times, and for a Christian production actually quite enjoyable (presentation rather than preaching). On the minus side it was rather let down by the KJV text & translation, which included sageist language (nowadays 'men' excludes children and women of the human race), along with Christians speaking as polytheists (viz that their god was a certain type of god, rather than philosophical monotheism which excludes having a god in the first place: if there is no god but God he cannot be a type of god). Though polytheism is embedded in translation and still speaks today, it can still hold cringe value and dampen enjoyment of a good film.
