Thought I'd look for Alvin and Emma in 1910,but I didn't see them either.
1900 Potsdam, Webster, Nebraska Alvin Mccoy 29 born Illinois father born Illinois mother born Indiana Emma Mccoy 28 born Missouri - married in 1892 - father born Iowa mother born Missouri Charles Mccoy 5 born Nebraska Fay Mccoy 3 Ruby Mccoy 1
Emma Alzada Brady McCoy died in March 1910 in Hastings, Adams, Nebraska.
June 1917 World War I draft registration Westerville, Custer, Nebraska Charles McCoy age 22 Home address Westerville, Nebraska Born 17 June 1894 in Braden, Nebraska Tall, slender, blue eyes, brown hair
Alvin has remarried by 1920. (Does this fit with the marriage certificate you saw?)
1920 Fanning, Scotts Bluff, Nebraska Albin B Mccoy 52 born in Indiana Mary Mccoy 52 Chester Scaggs 34  son-in-law Flora Scaggs 28 Jack L Scaggs 0 [1/12] John Mccoy 11