Did I read BTZS wrong
yep, the formula for arriving at an SBR from spot metering readings is:
Where D is the spread and N is the development required (N, N+1, N-1 etc.)
This takes into account the development you plan to use to calculate the correct SBR.
The spread plus 5 only applies to incident metering, not to spot metering. Since incident metering averages all light in the shadows, I find it strange that both your spot and your incident readings are the same, unless you were spot metering a gray card and not a normal subject.