I'm member of the ARRL so I take advantage of their Outgoing QSL service. Like most Bureau services it does take a long time for cards sent back but You can't beat the price. During a recent Ham fest, an ARRL card checker was in attendance and I planned to have some old QSL cards checked towards VUCC and I also explored the possibility of checking for WAC. I found QSL cards for all Continents except Africa which surprised Me. I have many EQSL and LOTW verifications but no actual sent thru the mail QSL cards from anywhere in Africa or surrounding area--Wow!!
I had a small QSL shipment from the W0 bureau last fall and decided to include some QSL requests for contacts from the African continent of which I had many but whittled it down to only contacts that actually mentioned Bureau replies. That does thin the contacts by quite a large margin but enough so I feel confident of obtaining some replies-- maybe several Years from now but thats OK !
73--Tim