Chris Willman Senior Music Writer and Chief Music Critic “Thanks for coming to my dad’s birthday party,” said Micah Nelson, a few songs into an all-star tribute to Willie Nelson at the Hollywood Bowl, attended by a sold-out house happy that Willie had found a way to schedule the 90th anniversary of his birth on a Saturday night. With roughly seven decades of songwriting and recording to commemorate, though, the party is stretching over two nights, bundled together and sold as a single ticket, where by the end of Sunday night everyone will have heard about 50 artists perform a total of about 75 songs. Ironically, one of the first numbers performed Saturday evening was young Texas country artist Charley Crockett doing a cut that Nelson had a hit with as a budding songwriter in the late ’50s: “The Party’s Over.” That title proved as un-prescient for Nelson’s career 65 years ago as it proved unprophetic for the scope of the Bowl celebration this weekend. But a little irony is always welcome in Willie’s world.