The term Multi Coating is in many ways a misnomer, some lenses had multiple coatings years before the term "Multi Coating" came into general use with Pentax SMC -Super Multi Coated", the critical word is "Super"
Ian, the photo industry has to some extent muddied the waters on the term 'multi-coating'. When coating ('single coating' ) was introduced, it was almost immediately applied to all air-glass surfaces within a lens. This shouldn't really be called 'multicoating'. The term 'single coating' properly refers to the fact that each surface only has one layer of material, usually magnesium fluoride. This does not mean that each surface looks the same colour. It would usually be necessary to vary the tuning ( in wavelength ) on the surfaces in order not to get a green-biased colour shift on the images. You can certainly see this on many lenses of the late-60's and 1970's.
Multi-coating
should refer to each surface being coated with more layers, typically three to five . This reduces the reflection value to less than 0.5% over a wider band, ie. over most of the visible 400-700nm band. People with more knowledge of the history of this can add to what I'm saying, but certainly Pentax were one of the first.
I am certain that all premium enlarger lenses from the early-90's are multi-coated - it was industry standard from this time.
Matt, the benefits of multi-coating are less on an enlarging lens ( with no bright solar source ) than for a taking lens, but still relevant. The multiple internal reflection from surface to surface do take something off the
local contrast within an image, as well as the overall contrast ( which can in B&W be compensated by an increase in the grade ) . It is in colour work that multi-coating helps more, because the inter-reflections take away some colour saturation, so minimising them on enlarging still helps.