What you see from sqlplus is what you get. The complete version display depends on Oracle and where they choose to have the patches update the version information. I ran into the same issue when I applied patches 1 and 2 to our 188.8.131.52.0 install. After the first patch it showed 184.108.40.206.1 but after the second patch it still showed only 220.127.116.11.1, not 18.104.22.168.5 like it should have. The readme.txt sent with the patch will tell you if it will change the version numbers.
Personally, I think it stinks. If I apply a patch, I should see it in the version numbers. How else are you going to know what patch you applied.