I'm not really sure exactly what your asking/saying.
As far as when I last bought an 870 from a store, I would have to say about 6 months ago. It is one of 8-10 I have now. I'm happy to post a picture of them if you need it. I have not bought a "new" 870 recently as I don't think the quality is there compared to older ones, so I cannot attest to what is marked on the receiver.
I agree, all 12 ga 870 barrels fit on all 12 ga receivers. (with exception of the SF without a bit of modification), as you mentioned. I don't think I said any different.
As for 870 20 ga as I mentioned, there are barrels that ARE NOT interchageable at all with all receivers.
They have never marked 2.75" or 3" on the receiver. Older (pre early 2000 guns?) had no marking on the receiver for 2.75", were marked "Magnum" for 3" and "Super magnum" for 3.5". Acceptable shell length in inches was marked on the barrel. And yes, i realize all those barrels are interchangeable with all receivers.
