Thanks for your responses. I actually asked the wrong question. I meant to ask whether we had to create a block reference in order to be able to store an attribute value (as opposed to just storing the value in the block). In this particular case I am storing the attributes of a "job" (aka order, aka project) and only need one instance of it. So I was hoping to just have to work with the block record without having to create a block reference.
Anyway, I came back to it this morning, with refreshed eyes and brain, and have been able to sort this out...so the answer to my revised question is yes, I can just use a block without any block references. That does leave that block open to being purged, however, so it's not perfect. But we have other AutoCAD automation software (COM based not .NET) that does the same and that doesn't suffer from any issues.