True, but it does place the massacre at '55. But as I've said before the official timeline consists of a number of flaws such as placing Vito's return to Sicily in 1927. See the related thread I made.

Over the years even the official timeline has differed a little bit such as putting Sonny's death at either '47 or '48. If you check out the Corleone family tree on the Blu-ray or DVD you will see that some dates slight differ from the timeline as well.

Also, on the criminal chart that's exclusive to the Blu-ray, it's stated at Michael Corleone's fact file that he ordered Roth's death in 1960, which would be correct since Roth came back to vote in the Presidential election.