How can I have alternating week numbers using a set date as week 1 in VB.net?

Question

I am using daypilot pro to generate a timeline. As per usual, we had the project built and finalised to spec when a spanner was thrown in the works. The department this tool was built for works off "week 1" and "week 2".

Here is a screen shot as to where we are.

You will see "week 6" in the screen shot, this is generated from the following vb.net code.

Protected Sub DayPilotScheduler1_BeforeTimeHeaderRender(ByVal sender As Object, ByVal e As DayPilot.Web.Ui.Events.BeforeTimeHeaderRenderEventArgs)

        If e.Level = 1 Then
            e.InnerHTML = String.Format("Week {0}", Week.WeekNrISO8601(e.Start))
        End If

    End Sub

What i want to do is generate alternating weeks, i.e. Week 1, Week 2, Week 1, Week 2. I will have to use a date identified by the department who want to use this tool as week 1, and calculate this going forward in the code.

Any advice or suggestions would greatly be appreciated.