When using old-style figures, what are the special cases of using lining figures (if any), apart from maths?
For instance, are reference marks one such instance?
Some 1998 text which references~
1998 would be in old-style, should the
 be in lining-style? i.e.,
Some 1998 text which references~$$
Same with equation number marks? How about percents?
In 1989, there was 25\%
In 1989, there was $25$\%
(side question, should there be a
\thinspace or something between the percent-sign and the numbers?)