There might be a problem with the birthdate and a computer searching database. I noticed in the Veterans Gravesite database your Thomas J Lisacek has a birthdate of May 28th 1918. The Social Security Death Index has a birthdate of May 28, 1913. If a clerk is using a computer search program that asks for a birthdate as well as a death date and either doesn't match, the computer software will not find the certificate. (Enlistment record also has born 1913)
The transcribing of records and indexes from court paper files to computer database is not fool proof. If the person at the court house is using an already computerized database, there could have been a misspelling of surname or the original paper entry was missed and as I point out the birthdates or even death dates might not match.
Even not using a computer for indexing has it's problems. I had tried, by mail, to get my husband's grandmother's county death certificate and was told they didn't have it. A cousin on a trip to the county looked for himself and found it as well as her probated estate papers. According to him, another person there doing research told him some staff given the task of finding records didn't always do the most through job of searching, especially if it involved going into the (dusty) oldest records room in the basement.