Достоверный факт состоит в том, что продление даётся на усмотрение офицера и давать оное офицер не обязан.
Продлевают часто, но далеко не всегда.
"If you’re unable to get a police certificate from a country, you’re responsible to show why you can’t get one.
To prove that you can’t get a police certificate, you must:
show proof that you requested a police certificate from the correct authorities and
write a letter explaining all the efforts you have taken to get one
Even if you send us the above items, this is not a guarantee of acceptance."