This is, Vo that is explained by Oxford, not Va.
I think there be a little confusion.
§ 23.1507
Operating maneuvering speed.
The maximum operating maneuvering speed, V
O , must be established as an operating limitation. V
O is a selected speed that is not greater than V
S √n established in § 23.335(c).
§ 23.335
Design airspeeds.
(c) Design maneuvering speed V
A. For V
A, the following applies:
(1) V
A may not be less than V
S √ n where—
(i) V
S is a computed stalling speed with flaps retracted at the design weight, normally based on the maximum airplane normal force coefficients, C
NA ; and
(ii) n is the limit maneuvering load factor used in design
(2) The value of V
A need not exceed the value of V
C used in design.
To summarise,
V
A must be equal to or greater than V
S √ n
V
O must be equal to or less than V
S √ n
You now see that Va relates only to control surfaces and their structure
Not so I'm afraid, I think you are misreading the intent behind § 23.423. V
A relates to the entire airframe.
Operating Manoeuvring Speed, V
O, is the maximum speed at which an aircraft in symmetrical flight at the specified flight weight and configuration will stall (unload) before exceeding limit load and sustaining possible structural damage. Aircraft are therefore aerodynamically g-limited by the lift line up to manoeuvring speed, and structurally g-limited by the load line above it. Manoeuvring speed is also the maximum speed for turbulent air penetration, although a speed somewhat less—fast enough to avoid stall yet slow enough to diminish the loads experienced—is usually recommended. (In an aircraft subjected to a sharp vertical gust of given intensity, the increase in structural load—and thus the acceleration the pilot feels—varies directly with airspeed.)
An example is the Cirrus SR20 which has the following Operating Manoeuvring Speeds (V
O).
2900 lbs 135kts
2600 lbs 126kts
2200 lbs 116kts