It's also my understanding that all of the well-known sedevacantist bishops make announcements regarding episcopal consecrations (and typically beforehand).
How about Bishop Kelly's consecration by +Mendez? They kept that under wraps until +Mendez had died.
There can be prudential reasons where for one reason or another it's not necessary or desirable to go public with the information. Now, if the SSPV had started sending priests out there who had been consecrated by +Kelly and the people were questioning who they were, then there's a compelling reason to go public with it. Until that time, why would it have been needed? Even then, I suspect that +Kelly may have played the card of ("I was consecrated in the Traditional Rite by a bishop who had himself been consecrated validly before Vatican II.") and asked everyone to trust him, and I imagine that most would have. I would have ... even though I disagree with him about many things, I don't believe he'd lie about it.
At the same time, the conditional of +Vigano is not in fact being hidden or kept under wraps like the +Mendez/+Kelly one, since when asked, Bishop Williamson did in fact affirm it to those who asked.
During persecution behind the Iron Curtain, there were a couple of clandestine bishops that Pius XII sent out there who were secretly consecrated (without witnesses) and were ordered to NOT disclose the consecration or any subsequent consecrations that took place there.
I think you're attempting to infer some provision of Canon Law or the equivalent ... where non exists. It's obvious that prudential considerations can play into whether to make such public or HOW public to make them, especially for conditional consecrations.
There's no compelling reason for you personally to know this ... other than curiosity. You may think that you have right to know, but you really don't.
At the end of the day, this sounds like yet another excuse to attack +Vigano. +Williamson had done another consecration that he didn't reveal until later, and +Kelly had his reasons ... and yet these other actions were not subject to the same degree of criticism.