Not to get into an argument over this, but this is not hearsay - I've been to the Register of Wills office in Pittsburgh and I've worked first hand with the death records they have. And here is what their website says about the availability of records prior to 1906:

"Birth records and death records prior to 1906 were not required reporting and therefore may be incomplete. Usually if the Estate does not list a death record it is not available."

And this is exactly what my previous note said. Death reporting was required in the city of Pittsburgh but not outside of Pittsburgh and Allegheny cities. So more often than not, you won't find a death record if the death took place in the townships, because the so-called Allegheny County death records are not death certificates, but just information copied from estate records, and most people who died didn't have estates probated. And apparently, even that copied info doesn't exist for 1904-1905. But again, if you haven't checked with the Register of Wills office directly (as opposed to the office that handles death records), then you should do so, as there may be an estate record (but not a death record) for someone who died in 1905.