In many GEO records associated with publications, I see CTCF ChIP-seq datasets without background controls—neither input nor IgG. Is there some accepted, different standard for CTCF that I’m unaware of? My understanding is that, in general for a ChIP-seq dataset, a matched input is necessary for a well-controlled experiment.

Or is this a kind of thing where CTCF ChIP-seq often have (apparently sufficiently) strong signal-to-noise that, historically, experiments have been considered acceptable without a background control? If so, I'm not sure I really understand the rationale. Lots of strong ChIP-seq signal can be arbitrary or technical in origin, which is part of why controls and things like exclusion lists (e.g., blacklists and greylists) exist in the first place.

Am I missing something specific to CTCF, or is not using a background control simply a fairly common practice for these datasets?