I just want to add a couple of things, I guess to my original post. First, I never, and I mean never touch my filters with wet fingers. My darkroom has a wet side and a dry side, and never the twain doth meet. Also, I always keep my filters in the box, actually in that Rolodex type thing with the index tabs. I don't think fading is an issue, but if it was, I would have expected the lower numbered filters to have faded more since they were used more.
One interesting thing is that with the Ilford filters, the 4, 4 1/2, and 5 are noticebly lighter; they are more pink, and clearly (to me) pass more light through. Hence the lower exposure required. The Kodak filters are the opposite. The higher numbered filters are darker, and definitely require more exposure. Regarding the Ilford filters, when I used the number 4 earlier this week, I checked the actual number on the filter, just to guard against my having misfiled one or more of the filters. I checked, and it was the number 4.
So I have two possibilities. One is to experiment with the Kodak filters. The other is to buy a new set, and I have already placed a bid on eBay. And speed matching is not an issue. I always do test strips, and I at least put a quarter or eighth sheet in for a test exposure when I change filters.
So I will experiment again next week or so, and I'll report back. Thanks again for all the comments.