Exception to the commutative law for addition!

I've been looking for years for an exception to the commutative law for addition [and subtraction], and at last I've found it! One way to state the commutative law is that

a + (b + c) = (a + b) + c

and I was always amazed to find that it held, time after time after time.

So you can imagine how excited I am to have discovered an exception:

Yesterday at midnight, Blogger bumped up my age from 63 to 64. That is,

[current year] - 1943 = 64.

But check this! I graduated from college in 1964. I was 21 years old. That is:

1964 - 1943 = 21.

But it is now 42 years later

[current year] - 1964 = 42

and

21 + 42 = 63, not 64.

That is, as an explicit exception to the commutative law:

[current year¹] - 1943 ≠ [current year²] - 1964 - 21.

...Oh, sh_t...(1) Blogger (obviously!) changed the calender. (2) And I didn't.