This is a brilliant blog post.

What happens if you write to the address listed in the GPL?

https://code.mendhak.com/gpl-v2-address-letter/

I wrote to the address in the GPLv2 license notice and received the GPLv3 license

I was curious about the 51 Franklin Street address in the GPLv2 license notice so I wrote to them as they said

@Edent Getting the v3 was a bug. The person requesting would have no way of knowing which version they needed. The software in question was obviously published under the v2 license, which has different clauses. That's the one that should have been received I think.