Well that's their problem, as I am telling you you have the right to go and ask for what is legally yours.
Most probably HR is not even aware of this fact, as only now some guys are coming up to the 4 years things since 2005/2006
They should go there and tell them to adjust it. Same was done by some FOs some months back with regards to another issue.
The problem here is that most people here have no spine and are too afraid to go and ask for something! HR knows this and is taking advantage of it, I know.
But this does not relieve someone from his responsabilty to go and ask for it!
Believe me, my basic salary WILL go up after 4 years.