lsh function documentation

[Ulrich Mueller]

The function documentation of lsh says:
| Most uses of this function turn out to be mistakes.  We recommend
| to use ‘ash’ instead, unless COUNT could ever be negative, and
| if, when COUNT is negative, your program really needs the special
| treatment of negative COUNT provided by this function.

I understand that lsh has no useful semantics for negative bignums
(bug #32463). However, old versions of the Lisp Reference Manual list
lsh and ash in the same section, and don't prefer either function:
https://git.savannah.gnu.org/cgit/emacs.git/tree/doc/lispref/numbers.texi?h=emacs-26.3#n811

So why would programmers who had used something like (lsh x 8) in their
code be called out for making a mistake?

Couldn't lsh's documentation just say that the function is deprecated
and that ash should be used instead?