最不动脑子的方法，直接写一个函数用错误陷阱捕捉就可以了

判断某个数组是否已经定义了下标，如果已经定义返回true

Function IsRedim(ByRef v As Variant) As Boolean
    Dim i As Long
On Error GoTo IsRedim_Err
    i = UBound(v)
    IsRedim = True
    Exit Function
IsRedim_Err:
    Select Case Err.Number
    Case 0
    Case 9
        Debug.Print Err.Number, Err.Description, "预定义错误"
    Case Else
        Debug.Print Err.Number, Err.Description
    End Select
End Function
'在模块中运行，以下过程测试IsRedim函数的效果
Function RunTest()
    Dim a() As String
    Dim b() As String
    ReDim a(5)
    Debug.Print IsRedim(a)  '返回true
    Debug.Print IsRedim(b)  '返回false
End Function

Function RunTest()
    Dim a() As String
    Dim b() As String
    ReDim a(5)
    
    Debug.Print Not a   '返回 -48665169 ，不是 -1
    Debug.Print Not b   '返回 -1 表示其未指定下标
End Function