It appears as if Shrader Lamberson later went by the name of Ottovan S., so possibly Shrader was his middle name.The evidence for this is in Civil War records at ancestry.com:
U.S. Civil War Soldiers database shows Shroader Lamberson in the 7th Regiment, PA Cavalry, Co. K
Civil War Pension Index shows Ottovan S. Lamberson in Co. K, 7th PA Cavalry - this was filed in 1900 in Missouri.
Another pension file shows his death on Apr 18, 1927 in Horton, KS.
His age is fairly consistent throughout the years, more than I can say for his name!I would guess that the pension record name would be more accurate than the census.
1860 Census - Mahoning Twp, Armstrong Co, PA
Isaac Lamberson, 46, farmer
Martha J., 39
Barbara A. 22, Shrader 15, Martha 13, Catharine 11, Isaac 7
1870 Census - Mahoning Twp, Armstrong Co, PA
Otuvan Lambuson, 24, laborer
1880 Census - Jefferson Twp, Ringgold Co, IA
Ottvon Lamberson, 35, farmer, born PA
Anna, 32, born PA
Charles 11, Elizabeth 8, George 6, Carrie 3 - all born PA except Carrie in IA
1900 Census - Upton Twp, Texas Co, MO
Otto Lamberson, born Feb 1846 PA, farmer, married 34 years
Annie, born Mar 1848 PA
George H., born July 1874 PA, farmer
1910 Census - Mission Twp, Brown Co, KS
O.S. Lamberson, 65, 2nd marriage, married 0 years, born PA, farmer
Mary E., 64, 2nd marriage, born MO
1920 Census - National Military Home, Leavenworth, KS
Octavan Lamberson, 75, widower, born PA, Company K
Related through the Boone family - Sarah Boone Lamberson was the sister of my ancestor Samuel Boone.