*Sigh* Another paper came out recently by another group in my small sub-field, whose work is pretty darn close to ours, and whom, despite 6 years of us citing their work in everything we publish, have NEVER. ONCE. cited ours.
Initially I was unaware of their work--despite thinking I had done all my due diligence and dug up everything potentially related when planning the project, I did miss their earlier paper on the topic, due to a keyword thing; being relatively unfamiliar with the field early on, I called it something different than they had called it and only searched for the terms that fell within my definition--and was corrected during review of my lab's first paper submission in this area. Since then, we've made a few new contributions, used different techniques than they do, and have always described their work with appropriate attribution of the fundamentals they contributed when we've reported our angles on the strategy our groups use in common. I have even met the PI in person--introducing myself and letting the PI know how much I like their work and that I have been following it for years now.
But either they are REALLY not watching their Web of Science citation lists, or they are deliberately choosing not to cite our research even in cases (such as this most recent one) in which it would be pretty appropriate to do so, since we previously reported a strategy that they report as a control experiment for monitoring essentially the same thing as we monitored in our work.
I feel like this must be getting to the deliberate stage--there are too many tools available now to know who is citing you and for what, and we really are about the only other group who regularly develops the kind of stuff we both work on. For them to have missed this is either because they're really out of touch or they really just don't care and/or are trying to ignore us/make sure we are ignored. But it's frustrating to know that despite doing the right thing, both from a professional courtesy standpoint and a scientific record standpoint--acknowledging the links that exist between work going on in different groups in a very small field--others might not behave the same way.