What you described was my impression as well. What atcroft pointed out is that if the original is v2 or later, then the GPL v2 requires that all original copyright notices be left intact. But if they are left intact, then you are distributing with a copyright notice that gives permission on your code that is v2 or later, which gets in the way of your intent to release v2 only.

It is a subtle issue, but my thought (since confirmed as a first impression by someone who knows a lot more than me) was that keeping the notices intact is not the same as keeping the copyright statement intact. Therefore as long as your copyright statement includes a statement that you are including work from XXX, and keep the original copyright notices in the file (while making it clear that they're not your copyright notice), you can satisfy the GPL v2 and not have to apply the original copyright statement to your code.

Cheers,
Ben