First appearance of the Silent Sisterhood

[Blood-worm's Master]

I wonder when did the Sisters of SIlence first appear in Warhammer background - were they created for the Horus Heresy CCG or are they mentioned somewhere in older publications (maybe in Rogue Trader, 2nd/3rd edition stuff or in WD)?

Does anyone remember/know something?

And fun fact: skimming through the Collected Visions today, I realised that all 3 of Sisters' depictions in Base Set of CCG are John Blanche's concepts. Only few months later, in Sedition's Gate (first expansion) there are 'normal' illustrations of them.

Likewise 'classic' Custodes with guardian spears appear only as members of command squads in BS (squads Vespason and Diocleton - btw I love how A D-B uses names from card game as inspiration) Again, we can find the first rank and file Custodes with spears in SG (15/120 'Centuron - Custodes Tactical Squad').

Edit: I found a promo card with something looking like lower rank, spear wielding Custodes ('Agricolus Custodian Guard Squad' - lovely art by Adrian Smith) from around the time of Base Set, so probably disregard the part about them.