A lot of universities don't mail to WES directly [like DU and MU], even on a lot of insistence, instead, they hand over the transcripts to students, who have to mail it themselves to WES, so they mail those documents through the post office nearest to the university or the one inside the university.
WES is already aware of what the universities and students are doing, hence, the secondary verification. See, it is the country in a whole that has to suffer, you are not the only one who is being subjected to additional verification.
And yes, WES will not disclose the recipients to you, if they do, it beats the whole purpose of verification and secrecy. Verification requests are sent to institutions via email and by post, post can take up to 15 days to deliver and since we are not aware to whom the email has been sent to, there is very little chance that the clerks might be aware if they have received an email or not. Also, most government institutions prefer replying to WES via POST instead of email, that adds up to more processing time.