IF OR Statements which always evaluate to TRUE - vb.net

Question

Recently I found an error which was due to the way I constructed an IF OR statement.
The original statement:
If a = 1 OR 2 OR 3 Then
`Execute code 1`
`Else if a = 4 OR 5 OR 6 Then`
`Execute code 2`
`Else`
`Do nothing`
The corrected code:
If a = 1 OR a = 2 OR a = 3 Then
`Execute code 1`
`Else if a = 4 OR a = 5 OR a = 6 Then`
`Execute code 2`
`Else`
`Do nothing`
So, the issue was the first part of the IF statement would always evaluate true regardless of the value of a, because it also evaluates the boolean value of the number 2, which is true. So simply spelling out that each number should be compared to the value of a fixes that issue.
My questions are:
1. When using an if statement and you have a comparative operation ( if a =1) followed by "OR 2", in what situation would you actually want to look at the boolean value of the number versus comparing the number against the value of the previously referenced variable?
Is there a way to identify if statements present in the code which will logically ALWAYS be true (and probably have a error)?
Edit: the_lotus pointed out that the boolean value of each number was not being evaluated but bitwise operations were performed between all the values and then a boolean evaluation was performed on the result. In this particular case it may be possible for it to evaluate either true or false depending on the value of a, though I am still interested in identifying if statements which always evaluate true.

Answer 1

As per your Edit, since you want to check if the value of A falls within a range, what you could do is store the ranges as an array and perform IndexOf to see if the value of A is in the collection.
Here is a quick example:
Dim a As Integer = 4
Dim collection1() As Integer = {1, 2, 3}
Dim collection2() As Integer = {4, 5, 6}
If Array.IndexOf(collection1, a) > -1 Then
Console.WriteLine("a = 1, 2, or 3")
ElseIf Array.IndexOf(collection2, a) > -1 Then
Console.WriteLine("a = 4, 5, or 6")
Else
Console.WriteLine("a is not a value between 1-6")
End If
Fiddle: Live Demo