One question that is a hard one to answer regarding the actors in our family is trying to determine where are they at a certain point in time. As in William's case, I have found him only in the 1910 and 1920 census records, when he was already in his 60s and 70s. So, where else can you find them?
I have used the newspaper articles found on Genealogybank, Ancestry.com, Footnote, and a wonderful site: Old Fulton NY Post Cards, which is free, and has remarkable articles esp from the NY Clipper, the Variety of its day, mostly late 1800's early 1900s.
One of the difficulties is determining the name they were using at the time, as they may use different names through their working years. In William's case, he was found as W.A. Lavelle, Col William Lavelle, "Cal" Lavelle, which was probably a typo of Col.
Another issue: were they married? Sometimes you will come across articles regarding their spouses, but that doesn't necessarily mean they were living together or working in the same state.
It is great to find 'official records' such as birth, marriage and death records, but as I have found those records that should provide answers sometimes lead to only more questions.
So what other resources have you used to trace your actors?