Greetings, Lackadaisical
Couple thoughts occurred to me - might be helpful, maybe not ...
As I'm sure you already know, the Dialogue "Filter For" box only works for "Objects" [NPCs, and Creatures] that are allowed to have Dialogue, by the MW Game Engine. A lot of time [e.g., for Alits] everything is just blank. For NPCs, they ALL get certain "vanilla, standard" Dialogue, based on race/class/Faction/Cell location, etc.
If you are making a mod, and have added dialogue, all of your new dialogue will be "asterisked" in the Construction Set (assuming you have it loaded as the "Active" file), so you can see if your Dialogue actually got "saved" last time, or not (whether you view the Dialogue "filtered" or "unfiltered").
As I'm sure you also know, the CS really doesn't want you to add "new" Dialogue while the Dialogue Tree is "filtered." [Pain in the butt, I know, but, there you are ...] The Dialogue Tree is this one, gigantic database ...
So, my first thought is, if your Dialogue entries don't show up at all (unfiltered), or if they show up "unfiltered," but not when "filtered" for that NPC, you probably need to look closely at the parameters you have set, for that Dialogue to appear. Mis-spelling of the NPC's name (ID) is a typical silly example. Another is, if you added Dialogue for (e.g.) "Snowy Granius" but set it for Race=Dunmer [he's an Imperial] or Cell=Ald-Ruhn, Ald Sklar Inn [he never goes there], it will probably never show up. And, quite likely, the CS (when you ask it to "save") will say to itself, "Self, this silly hu-man is trying to do something utterly ridiculous. We ain't puttin' this foolishness in our database, Nossir! Not today!"
And, it never really gets saved. In other words, down to "Operator Error."
The other thing is, if you are doing your "evaluating" with other 3rd-party mods loaded [and, if they are not "active," their Dialogue changes WILL NOT be "asterisked"] .. Well, you don't really know what they may be doing to your Dialogue Database, do you? Unless you have previously anolyzed them, and possibly repaired any glaring errors beforehand?
Uh Huh! Thought not...
But, I'm sure Jac's advice will be helpful to you. He's very good at Dialogue.
However, if you could clarify what, specifically, you are trying to accomplish with your "Filter" efforts, perhaps we could provide more useful feedback for you, than just "general" comments???
Happy modding!
DARoot