Perhaps it might be worth clarifying what sort of "pt" does LilyPond use. Or
did I just overlook this information?
For instance, run
\version "2.25.12"
\pointAndClickOff
\header { tagline = "" }
\paper { text-font-size = 12 }
\markup { LOL }
and either use -dbackend=cairo --eps, or produce standard PDF and decompress
it (e.g. with qpdf). Look for the BT command in the resulting file. You'll
find that the font size is actually ca. 11.9531, not 12. This would suggest
that the unit used is rather the TeX pt (1/72.27 in) instead of the
PostScript pt (1/72 in).
The difference
12 * 72 / 72.27 - 11.9531
is quite close to 2/1024, again, although not convincingly close.
AS
