And so the BBT gets another "free parameter" to tune it to observations. This parameter is a "special type" of dark matter that is different from the dark matter that exists today. This special type "decays" and emits photons that directly interact with hydrogen molecules.
Of course, regular matter that decayed on the same time scale could also do the "prevention of cooling" that is hypothesized. But, according to the BBT, no regular matter other than hydrogen and helium (and maybe a bit of lithium) had evolved yet when this effect is "needed" by the BBT.
But, that raises even more questions about how some additional type of "dark matter" that can decay at the needed time and rate could have been "made" by the BBT when regular matter was restricted to just the lightest isotopes.
If you can just make up new stuff and put it into a theory, you can make the theory do anything - except have credibility. With 95% of the BBT now being stuff that is not detectable or provable, there is a real credibility problem.
The BBT seems to be group think that is stuck on the concept of backwards extrapolating the apparent expansion of the universe at the current time to show that the universe started as a tiny, if not necessarily infinitesimal point in space.
I have to wonder what people could come up with as competing theories if they abandoned the goal of proving that everything really could have started at a tiny point-like volume of nearly infinite density and energy level.