Not true
Providing that the AFM data is observed and the sums done correctly with respect to the AFM, the background certification stuff will be taken care of transparent to the user.
If VR is below V1
The AFM will never let you do that. Ergo, a mistake along the way.
However (and we don't do this for the obvious Standards reasons) providing the brake energy is OK and the ASDA adequate, the physics will permit such a non-SOP action.
When would you ever want a V1 which is 'artificially' lower than the highest V1 that you could safely use? In effect it commits you to 'go' when you could actually comfortably stop. When is that ever going to be advantageous?
If the risk assessment is such that one is more concerned about stopping than going. It is essential to keep firmly in mind the fact that the AFM and certification, generally, is based on probabilities, not guarantees.
It is held, generally, that a high speed abort, even with a generous ASDA pad, is a high stress, high risk business ...
Sometimes, the flight standards assessment is that a lower V1 might be a better option .. in general, more risk of killing yourself stopping than going.
Increasing (stop - my addition) safety margins...
Who says you can "comfortably" stop from V1?
Precisely.
Contaminated surfaces significantly complicate control by increasing the actual Vmcg.
How so ? Vmcg is based on nil nosewheel steering input and the numbers consider friction characteristics.. it may be prudent to consider a reduction in crosswind limits for tyre force considerations .. However, a low speed go decision can provide an interesting piloting experience.
On that point, crosswind from the "wrong" side will increase the real world, on the day, Vmcg.
therefore they use the lowest V1 available.
Choosing the lowest V1 might introduce some exciting handling in the go case .. very much needing sim exposure and practice to reduce the startle factor. However, somewhere in the middle range makes more sense than routinely going at max V1.
I recall a period instructing on a 732 sim which had had the rudder mod incorporated ... very much a handful for the pilot at critically low speeds .. but trainable with exposure. Just how valid the observations might have been for transfer to the real aircraft I don't know .. but the stick and rudder exposure certainly upped the ante regarding instrument scan rate in the continued takeoff case.