I don't know how is implemented DW but this is a very common problem in programming and there are two ways of solving this: the one you have said and the one using counters. For each user, you can have a field with the count of every public entry and another field for the count of every access entry. If the user have filters, I suppose they are listed in a table so, adding a field for "entry counts" will simplify the queries at the DB.

I know that this solution has it cost. It needs more space and being updating those fields every time a user post an entry. But then you only need to check a few fields to know the exact number of entries a user can see depending on his or her security level.

Like I said before, I'm not sure if all this work is worth just for a small detail, that's why I suggested the option of just hide it (if the user want it). And, despite all the comments I have read here, it seems to me that the only problem I'll have having hidden the numbers of entries and "last updated" date, is that they won't trust me at the time of giving me access to their entries, just because they don't know if I update my journal frequently. In my opinion, that's a risk I can take.