My limited opinion/view -- you have to factor many things when considering how often you/we should trim. How you comb and/or handle your hair. What combs you use. Styling products. Moisture/protein balance. Are you on top of your moisturizing/sealing game. Etc. Etc.
I went an entire year without trimming because I was in between stylists. While I maintained a good regi and gained a lot of length, I lost a good bit of it to. Out of nowhere, I started having split ends and mid-shaft splits. I protective style frequently so my ends are not really subjected to the weather all that often. However, I think my issue was a three headed monster - not using seamless combs, using a tangle teezer to detangle on several occasions and holding on to aging ends that needed a trim.
I now use seamless combs, handle my hair carefully and have kicked the tangle teezer to the curb. I will be incorporating trims several times per year going forward to ensure aging and/or unhealthy ends don't split/tear and travel up the shaft and cause additional issues.