This has been discussed here a couple of times already (but I can't find the link). It is evident that the process by which UA passes along flight info to Hilton had a glitch that affected flights taken the week of 6 September (I'm missing 4 flights, for 16k miles). I called UA several weeks ago, and they said they would take it up with Hilton via fax (see how being 1K makes a difference?) After waiting for several more weeks, I gave them a call last week. After the obligatory hold to talk to the supervisor, the agent told me that they had sent a fax to Hilton (I hadn't mentioned it) and that they would follow up on it again. I'll give them another week and then call again.

Since there are several FTers in this same situation, we should collectively lean on UA to get this resolved.