Travispatra
Yes Vesak is the one major holiday in Buddhism, though I think the reason mainstream Buddhism doesn't have so many holidays is that the traditions that follow are seen as "attachments". Does anyone agree with me on this? That, and because of the local influences as the religion moved around - there are many, many discrepancies.
Rohatsu was December 8th. That's the Japanese equivalent of Vesak, which is in May.
It's like having a denomination of Christians celebrating Christmas in April or May.