I was raided by a small band that went straight for an Excavation site. I wiped them out, and a few months later they came back and did the same. Both times, when the raid was over, there was no notice of the raid statistics or that it had even ended. Just the raid symbol in the top left turned off. This video captures the second raid just months after the first.
Edit: After a 3rd group came a couple months later (also just 9 raiders) doing the same thing, I position my men closer to the Excavation site, and as they showed up, suddenly I was targeted by 3 more raiding groups (4 in all) with a total of 40 raiders from all sides of the map. Just as I wipe up the larger raid, another party of 9 comes down the same path to the Excavation site.
Edit 2: This party of 9 seems to be stuck in a perpetual loop. I’ve tried killing them off before they get to the Excavation site and that didn’t fix it. I suspect a save and reload might, but I’m gonna milk this for the troop experience for now.
Edit 3: I just discovered that if I put my troops where the raiders spawn, they spawned in a different location lower on the same left side of the map and headed to the same spot. Defeating them from this spawn point did not end the loop.