Not a common use case but if I do for example:

| $ b4 prep -F 20221117104636.639889-1-broonie@kernel.org -n tap-spec-relax -f v6.1-rc1
...
| NOTE: any follow-up trailers were ignored; apply them with b4 trailers -u

I run the suggested command but get:

| $ b4 trailers -u
| Calculating patch-ids from commits, this may take a moment...
| Checking change-id "20221207-tap-spec-relax-9138e5760340"
| Grabbing search results from lore.kernel.org
| Nothing matching that query.
| No trailer updates found.

since the change wasn't sent with b4 initially.  I see that the
documentaton does say to use -F but using that produces the same
output, it looks like it's checking the change-id no matter what
and gives up if it can't find it.

BTW I also notice that no template inter-version chnagelog is
generated for the b4 prep command above, the same thing seems to
happen even if the sent series has a cover letter.