Hi,
I have the question: is anybody aware that patches in a recipe are not
fully applied?

When retrieved the archive for package unpacked.
Аttributes of multiple files are set as readonly.

For 5.30.1 https://www.cpan.org/src/5.0/perl-${PV}.tar.gz;name=perl
or for 5.22.1 and 5.22 and 5.20 http://www.cpan.org/src/5.0/${BP}.tar.xz
lots of read only files in archives.

Form  man of Patch behavior --read-only=warn by default.
So files to be patched with read only attributes remain unchanged.

For override patch default behavior on --read-only, i placed in
poky/bitbake/bin file with name patch and content:
#!/bin/sh
/usr/bin/patch --read-only=fail "$@"
exvar=$?
echo "patch wraper readonly fail" "$@"
perror $exvar
exit $exvar

And as a clearly predictable result, the build of perl failed.
To fix problem and apply all patches and particularly my patch to backport
issue for my host environment
I added to perl_${PV}.bb recipe this:
do_patch_prepend() {
    os.system('chmod -R +rw %s' % d.getVar('S'))
}