score:20
The 1976 date appears to be a transcription error. Not only is the 1970 date more frequent in English literature, the two Russian language sources below (that appear to be independent) agree on a death date of June 12, 1970.
Numerous other Russian language sources also give 1970 as the year of death, but I saw no reason to believe these were independent of the two above. I found no Russian language sources (of about 12) that listed 1976 as the year of death.