I can't give you an exact answer specifically why yours is marked one way his is marked another, other than the of course newer/older changing it up a bit, they probably just changed it up a bit.
However I will tell you I got sucked into Express myself without realizing , I bought an "870 Tactical" off the shelf at D!cksSportingGoods in October... I thought because it had "870 TACTICAL" engraved it was an upgraded model or non-Express etc. Nope not at all. Remington went to the Express (Wiki says "by 1996 spurred by the Express" who knows when it actually started, I once heard the 70s?) and almost ALL their guns are now Express, unless specifically marked and marketed as Wingmaster or Police etc.
My finish is absolutely terrible, I mean TERRIBLE. I assumed it was a little dirty and had been handled as a display model and they hadn't any more in the back "but we just put that one out" in fact it went out in April and I bought in October lol. Within a week of owning it it had some marks and scratches, first range session marked it good, now it looks like a real combat shotgun, its borderline needing to be refinished soon. I probably can get Remington to honor its warranty but, its like a 12-20 week deal, for another TERRIBLE Express bluing job... I am probably going to pay and do it professionally, I want it Parkerized but locally I can only find ppl who Cerakote.
The good news is , other than the finish, an Express is a Wingmaster is a Police- Wingmaster these days just have beautiful bluing finish and beautiful furniture, and the Police has also better (parkerized) finish, specific furniture, and 3 different parts than the Express (carrier latch spring, magazine spring, non-MIM Extractor, I did all those replacements plus the oversizes safety). So an Express is still an 870, still the gold standard of worlds best shotgun (Although I am a Mossberg man firmly before I ever bought an 870, its still a famous gold standard.).
The old , original Remington Wingmasters and Police shotguns are THINGS OF BEAUTY. But, Remington is no longer Remington, its Freedom Group and Cerebrus Captial Managemnt etc. And the shotguns today are just not as nice, not the same. Old 870 Wingmasters and also 870P's , are just REMARKABLE.