Just a side note . . . The Christians I know do not celebrate the death of Christ, they celebrate the resurrection. In the context of history, the death was nothing special. The Romans were killing up to 700 Jews a day by crucifixion. It was the resurrection that was the miracle.
The Witnesses see importance in keeping the commandment to "keep doing this" (eating and drinking) while they ignore the command to sell all and give to the poor.
If the Witnesses wanted to follow Jesus, they would need to follow and practice Judaism . . . . for starters.
You are right on the Watch Tower Publishing Corporation's error of dates. By my secular calendar, the first day of Passover is April 17th in the usa.