Many state parks still have "No Firearms" signs. This is because when the bill was introduced to allow carry in state parks, if signs had to be taken down or modified it would have added a fiscal note to the bill and many opponents would have used that as a reason to vote against the bill. So it was amended so that parks were not required to do anything with signs...said it still applied to those without a permit...like anyone without a permit could have carried anyway..but I digress.
It is good to hear that they replied to your query and gave you the correct information.
If I remember correctly....when normal maintenance requires a sign to removed or repaired, the new sigh should not have "No Firearms" on it or if it is a No Firearms sign only, not be put back up.