In most cases there is a range of acceptable V1 values. Perhaps this was such a case. Then the FMC is likely to calculate a V1 based on stopping and acceleration distances only, then adjusting the calculated value to ensure >Vmcg and <Vr criteria.
The exception, where there is only one acceptable value for V1, is the balanced field scenario. It's often not applicable to real airfields, where:
- the TORA is only just big enough for the "stop" case; therefore V1 cannot increase without increasing stopping distance unacceptably, and
- the TODA is only just big enough for the "go" case; therefore V1 cannot reduce without increasing post-engine failure acceleration distance unacceptably.
There are others on PPRuNe with much more knowledge than I. But perhaps this will help until you get more thorough advice.