Gentlemen:
If I may add my own experiences here. Indexing issues are not limited to Norico’s, and it has become my policy to try a specific barrel on a particular receiver for fit and index before purchase. Allow me to explain.
I am an aspiring trap shooter, and for 16 yard singles I prefer to use an 870 Wingmaster built with hand picked parts. Back in 1995 before they were commonly available locally, I wanted a standard contour, vent rib 30" barrel with Rem-chokes, mid bead, and Bradley type front bead. I had a good friend import exactly such a barrel as well as a release trigger from the states for me.
At the time I was using a late 1970's early 80's (per-flexi tab) receiver that while solid and functional was not very pretty. When I mated the barrel to the action, the barrel indexed well. And I continued to shoot.
Along the way I sold that original receiver, and found an all steel 1960's receiver with nice bluing and great machining that I just had to have. When I attached my imported barrel (mid 1990's production) to that receiver, the barrel was out of index very badly. I tried to use it for trap but my scores suffer.
In the end I had to find and purchase an early 1970's production 30" Vent rib fix choked barrel to index properly with the 1960's receiver, and purchase a pristine late 70's/ early 80's reciver to go with my very expensive imported barrel.
The moral of the story, try before you buy, and realize that as things and time progress, manufacturing tolerances will invariably change.
Just my 2 cents, and your milage may vary
Regards and all the best
AbH