I ran this in Excel 2003 and didn't have an issue.  

Sub AddNewChart()
   Dim x As Variant
   Set x = ThisWorkbook.Sheets.Add(Type:=xlChart)
   x.Name = "NewChart"
   Set x = ThisWorkbook.Charts.Add
   x.Name = "NewChart1"
End Sub

Sub CheckSheetType()

Debug.Print "NewChart1", ThisWorkbook.Sheets("NewChart1").Type
Debug.Print "NewChart", ThisWorkbook.Sheets("Newchart").Type
End Sub

Both came out Type = 3

When I tried it in Excel 2007 before saving the file, I got the same thing.  
Also no problem if the workbook was an .xlsm workbook.  

I tweaked my code a bit to see what I'd get for other things.

Sub AddNewChart()
   Dim x As Variant
   Set x = ThisWorkbook.Sheets.Add(Type:=xlChart)
   x.Name = "NewChart"
   Set x = ThisWorkbook.Charts.Add
   x.Name = "NewChart1"
   Set x = ThisWorkbook.Sheets.Add(Type:=xlExcel4MacroSheet)
   x.Name = "Macrosheet"
   
End Sub

Sub CheckSheetType()

Debug.Print "NewChart1", ThisWorkbook.Sheets("NewChart1").Type
Debug.Print "NewChart", ThisWorkbook.Sheets("Newchart").Type
Debug.Print "Macrosheet", ThisWorkbook.Sheets("Macrosheet").Type
Debug.Print "SHeet1", ThisWorkbook.Sheets("Sheet1").Type
Debug.Print "Sheet2", ThisWorkbook.Sheets("Sheet2").Type
Debug.Print "Sheet3", ThisWorkbook.Sheets("SHeet3").Type
End Sub

I only got -4167 for the regular worksheets.

Have you tried using something like this (for separate worksheets in the
workbook

Sub TestChart()
Dim myChart As Chart
For Each myChart In ThisWorkbook.Charts
   Debug.Print myChart.Name
Next myChart

End Sub

If the Charts are embedded in the worksheets, it's a bit different.

Dim myChart as ChartObject
Dim WS as worksheet
for each WS in thisworkbook.worksheets
  For each myChart in ws.chartobjects
       debug.print mychart.name
  next mychart
Next WS