Finding primary sources on this seems to be pretty hard given the general level of misinformation from some of the sites. As best as I can find it appears that milk was used in at least some paints through the 1500's after which time it was mostly abandoned for some period of time in favor of oil paints.

An example of a fairly trustworthy source detailing the use of "tempura" which is arguably a form of milk paint (although you could also certainly claim its egg paint, although it appears that some tempura's were heavier in casein content than egg or only used casein in some cases so) in the 1400s
http://www.visual-arts-cork.com/old-...botticelli.htm

According to this article it was "rediscovered" in the early 1800's precisely because of a lack of linseed oil during the french revolution.
http://www.historicnewengland.org/pr...les/pdf153.pdf

Also managed to find this doc which is my best source to date from the Getty and williamsburg on historical paints (apologies for the sketchy looking url, I'll excerpt the most relevant bits for this discussion but the doc is a gold mine of information on historical pigment/binder usage):
http://d2aohiyo3d3idm.cloudfront.net...0892365013.pdf
Of interest are pages 42 which states:
"Casein
The early history of casein in paints is sketchy. Ancient Hebrew docu-
ments reportedly mention its use (Gettens and Stout 1966:8). Cennini’s
The Craftsman’s Handbook (1954:68) mentions the use of casein glue but
does not mention casein paints. Lime casein was reported to have been the
medium of some late-twelfth-century wooden panels from the ceiling of
a church (Denninger 1969). Casein paints, which were produced in the
United States on a commercial scale beginning in the late nineteenth cen-
tury, were apparently very popular in interior and exterior house painting
throughout the nineteenth century, probably popularized by a late-
eighteenth-century French book that appeared in translation just after
1800 (Phillips 1994:253). How extensively casein paints were used, and
what the specific formulations were, can be understood only by analysis of
paint samples. Virtually no detailed examinations of these paints have been
published to date."
Followed by a description of the composition and behavior of milk and casein in paint. Summarized snippets:
"If whole milk were used, the dried paint would contain all of the
components of the original milk. Drying simply involves evaporation of
water. As the water evaporates, the protein micelles become denatured.
This is an irreversible change, mean-ing the protein micelles are no longer
soluble in water after drying. However, the milk sugar component remains
readily soluble in water;thus, such a milk paint would probably be easily
damaged by water."
And
"A purer casein paint could be produced by beginning with curds, which are precipitated
from soured milk and are rich in casein (the casein micelles become unstable under
acidic conditions). Washed, dried, and ground curds are largely insoluble in water but can
be solubilized by the addition of a base. Drying of such a casein paint involves
evaporation of water; if a volatile base (such as ammonia) has been used, the
protein will precipitate as the water and the base evaporate. If a nonvolatile base is
used (such as lime), the cation of the base (calcium, in the case of lime) reacts
with the protein molecules during drying to form highly insoluble calcium-protein
complexes; reaction occurs at the phosphate groups on the protein. Depending on
formulation, a casein paint could remain read-ily soluble in alkaline water or could
be virtually insoluble after drying. If skim milk were used for the curds, the
resulting paint would contain little if any of the original oil or fat component but
could still contain some milk sugar"

There is also reference to "Nathaniel Whittock's The Decorative Painters’ and Glaziers’ Guide(1827:57)" in which it is stated "Alternate glazes in distemper (animal-glue medium) are described. Both were to be followed by second glazes of whiting ground in milk, and dark veins in Prussian blue".

The commentary on how some pigments would react (poorly) with a milk base are also illuminating:
"This consistent use of Prussian blue in oil disproves a popular theory
among folk art collectors and dealers that many of the “dry-looking”
blue paints were milk-based. It is highly unlikely that any blue paint
containing Prussian blue would be a milk-based paint, as the high pH
of a casein or milk-based paint would rapidly discolor the Prussian blue to an
unsightly brown."

It also appears that it may be difficult to differentiate some of the different protein binders after sufficient time has passed so a lot of the research is still needing to be done.

One would have to assume that there was some residual use of casein binder in paints and glazes ongoing, but it might well be sparse or highly regional depending on what the folks in that area knew about.

There is also likely some confusion because the lime washes were sometimes referred to as lime "milk" although no milk was (usually? ever?) used.