Honestly in that case I think you did right by your readers. I did the opposite once, I tagged for A/C because there was a mention of it having happened in the past but not currently in the frame of A/B, and I got a load of nasty comments from A/C shippers who were angry that I dared insinuate that A was not monogamously soulmate bonded with C. Or B, for that matter. I had to eventually go back and tag it for "nonmonogamous relationships" because holy fuck purity culture is out of control and in 20 years of fandom I have never gotten hate like that for any level of bicycle shipping.

tagging in general is a damned if you do/damned if you don't situation but I feel like most of the time, when you tag, someone either wants to find it or they want to eliminate it and the tag system allows for both. Tag it Omegaverse so A/B/O fans can find it and haters can block it, it works just fine for both. Really, the amount of mention a relationship/pairing/character is in the story is the only gray area for tagging that I can think of atm.