So I was watching some videos. Over [here][1] Padmanabhan claims that in a zero cosmological constant universe setting $a =1 $ in the FLRW metric is quite non-trivial:

so there is a constant in the universe which you can determine

only if this $a_0$ is given but the Friedmann equations do not fix

$a_0$... Friedman equations with no extra physical input you will never

be able to figure this out

Sorkin makes a similar point [here][3]:

it has an arbitrary normalization; it no longer has a direct physical meaning. It's only the ratios of $a$, sort of $a$ at one time $τ_1$ to $a$ of $τ_2$ that have meaning.

I know while there were some solutions of General Relativity which are pathological from the initial value problem's formulation. I didn't think FLRW was one of them?

The initial value problem then consists of specifying initial data for

all fields on one such a spatial hypersurface, such that the

subsequent evolution forward in time is fully determined.

Like naively I'd think that the initial value data corresponded to something physical? I feel something is amiss? Because if I take limits and go to a Newtonian mechanical regime I've never heard someone make similar claims for a fluid?