All fields are required.
Most Class A offices have full maintenance elevator contracts. In theory, that means that the elevator maintenance contractor is supposed to maintain the elevator according to it's original specifications throughout the life of the contract. The only thing that should be a problem is parts obsolescence.
In reality, elevator maintenance contractors can often be stretched for time. When searching for a maintenance contractor, make sure to do due diligence. Among the questions to ask: How long as the contractor been in your market? How many other elevators does he service? How many staff are in the market to handle the elevators?
The number of staff and elevators a contractor is responsible for can tell you whether you're going to have a potential problem with making sure your own units are properly maintained.