Net Present Value of Sequestration in blue carbon model

In the blue carbon model,If I enter the layer years 1990,1995,2000,2005. . . . . According to the formula in the documentation, the 1995 carbon value is calculated from the 1990-1995 net sequestration, and the 2000 carbon value is calculated from the 1995-2000 net sequestration. . . . .
So I want to know how the carbon value of the base year(1990) in the layer output from the model is calculated?

And I have another question, can the value of blue carbon only be calculated for sequestered carbon? Can I use this software to calculate the blue carbon value of the total carbon stock? How am I supposed to do that?
Thank you

The model only values changes in carbon storage (emission/sequestration) over time. This is due to: 1) the way social cost of carbon methods and carbon markets value carbon; 2) estimates of the value of non-marginal changes to carbon storage generally become more implausible as they get bigger, as with all ecosystem service values (Bockstael et al., 2000)

If you insist on valuing the total carbon stock, I believe the model can accommodate if you simulate future landscapes as having no carbon storage potential.