Here's an unofficial coin that was slabbed. It's in pretty good style and managed to slip through as official.
Official means that a coin was struck by a Roman mint. Unofficial means that it wasn't struck by the mint. http://www.constantinethegreatcoins.com/barb2/
Two things should immediately give this coin away as unofficial...PTR as the mintmark, though it should be more like TRP. The standard has an X even though this is only used from Arles. Lets face it (pun intended) the thick, heavy, bust is not right. On the reverse, the phalera, metal sculpted discs on the banner are just not right. The letters are not quite right either, though it is spelled right, and note how the soldier on the left is planking all the way to the left. It's a delightful coin and I am delighted that it got slabbed...I usually break them out, but this one I will leave in. This coin is a delight and I love it....one of my new favorites.
It is just my opinion but I believe it would be a mistake to break out any NGC error slab. They make so very few errors that a coin being one is elevated to a special level collectable in its own right. I only own one coin still in a slab. It is one of those 'other' brand slabs that makes enough errors that there really is nothing there to see but I still keep it sealed to show people that we collect coins not the labels someone stuck on them. Unfortunately I am terrible at photographing coins in slabs but that might be from having so little practice. It might be good to mention that this mint did use PTR for the issues before the two soldiers, two standards type that preceded this one standard version including my campgate. Hey, at least NGC read the legend correctly identifying Constantine II while NNC failed to note the difference an N makes in my coin that is the only reason I would buy a slab of theirs in the first place. Those who have been paying attention here on CT may recall one of our number posting an NGC slab containing a now infamous and very common fake. My example below was given to me by the seller when he refunded my purchase. I gave it away so it now resides with the one in the slab. That collector has better evidence whether or not the two coins are fakes. If the NGC coin is the mother of mine, might we see a trace of its encrustations reproduced on my coin? Who remembers this thread? What happened to the valued member who posted it? https://www.cointalk.com/threads/source-coin-of-the-carisius-counterfeits.322219/#post-3665248 Be sure to read how David Sear is mentioned in that thread. I would really like to know details of how that fake came to be in an NGC slab. To my way of seeing it, I'd rather have that slabbed fake than a genuine denarius of this type. We all make mistakes. Some people make a few mistakes and get mentioned in Coin Talk. Do you have any idea how many people have published on Einstein's errors? One: https://astronomy.com/news/2018/09/5-times-einstein-was-wrong
The mintmark PTR and STR is quite common on official Trier-coins of Constantinian II and Crispus, but I guess you mean the GLORIA EXERCITVS type where it does not normally occur.
If anyone was wondering what an unofficial coin slab looks like, I have two examples...though I took these out.