It's a scandal that we have to rely on hearsay to know whether someone has been conditionally ordained.  This should all be published publicly on the SSPX website.  There's been a long history in the SSPX, predating the neo-SSPX of performing conditional ordinations in a "hush hush" manner.

There was a time in the mid-1990s where a mysterious "priest" (Father/Mr. Belland) showed up at STAS and was offering Mass at the main altar.  Both my brother Steve and I went digging to find out who he was ordained by.  He was in fact a Novus Ordo "priest".  But after digging we found that there was a secretive conditional ordination ceremony done.  We only found out by word of mouth from the sacristan who set up the bishop's chapel for the conditional.

But that was not always the case, as in some instances the NO presider refused conditional ordination ... at which point he should have been shown the door.  In fact the case of one "Father" Stark was a huge reason for the split of The Nine.  Tragically, Archbishop Lefebvre sided with Stark and allowed him to continue simulating Mass at SSPX chapels and instead showed the Traditional priests the door for refusing to accept that.  No, the split of The Nine was NOT about sedevacantism, as is popularly (and incorrectly) believed.

That's all due to politics with the Novus Ordo.  We can't say that the NO Rite of Ordination is doubtful or possibly invalid because that would be to impugn the Conciliar "hierarchy".

Of course, if there's no positive doubt, it's a sacrilege to perform even a conditional ordination.  But if a conditional ordination is permitted, then there's positive doubt, and it's REQUIRED to perform one before subjecting the faithful to such dubious priests.  So the faithful have a right to know.

This nonsense has plagued the SSPX since its early days I'm afraid.

One incident that does amuse me, however, is the conditional ordination of Father Carlos Casavantes.  It's amusing because he was "ordained" to the priesthood directly by JP2 in Rome. 

Any word on Fr. Deister of Our Lady Immaculate Church in Oak Park, IL?

I too am very concerned about Novus Ordo Priests functioning in the SSPX without being conditionally ordained.

One other option some might have is that, if you're questioning whether a particular former Novus Ordo priest has been conditionally ordained, is to find some way to contact Bishop Williamson and ask him. Back when he was active in the SSPX I was told he "saw to" the conditional ordination of many of the Novus Ordo priests working with the society. He's obviously been out of the mainstream SSPX for a while now but if the former Novus Ordo Priest in question (such as Fr. Pieroni) has been in the SSPX for a while Bishop Williamson might have information on whether a conditional ordination was done; at least if he was the one to do it.

Why don't you just email Fr. Pieroni? If you one S>S>P>X priest email, you can easily guess what it is.