Timeline Error in "The Night of the Lord of Limbo"

I try not to nitpick on this series, I really do, but every once in awhile I need to speak up. In Season 2, episode 15, "The Night of the Lord of Limbo," an incident during the Civil War is spoken of as having occurred seven years earlier. Two previous episodes, one in Season 1 and one in Season 2, have established the year as 1874, and since this is well along in Season 2 it could even be 1875. The Civil War ended ten years earlier, in 1865. What's more they are speaking of an incident which occurred earlier in the war, around the time of the Siege of Vicksburg, which was in 1863, so the event should have been twelve years earlier, not seven, unless this is supposed to be a flashback episode taking place before the main timeline, or unless the Lord of Limbo has been messing with time so much he doesn't know how much has passed. Presumably this was either done so as not to make Jim West too old, or simply because the right hand often doesn't know what the left hand is doing as far as what year it's supposed to be in a TV series.