Does the Seal of Confession include saying whether or not a person confessed to them? The Seal of Confession is the duty of Catholic priests to not disclose anything they hear from someone who comes to them for confession. Does this include disclosing whether or not someone has seen them for confession? For instance, could they say:


  Yes, I have seen Joe Schmoe in confession yesterday afternoon, but I cannot reveal anything that was discussed.


Or would that be something that they wouldn't be allowed to say?

Another way of putting this is: at what point does the Seal of Confession start? When they walk in the door or when they say something?
No, a priest cannot even reveal that because it would betray the penitent.

Can.  983 §1. The sacramental seal is inviolable; therefore it is absolutely forbidden for a confessor to betray in any way a penitent in words or in any manner [e.g., by signs] and for any reason.
Can. 984 §1. A confessor is prohibited completely from using knowledge acquired from confession to the detriment of the penitent even when any danger of revelation is excluded.§2. A person who has been placed in authority cannot use in any manner for external governance the knowledge about sins which he has received in confession at any time.

Technically, a priest can reveal good things about a penitent he has heard in confession. This is what St. Catherine of Siena's confessor Bl. Raymond of Capua was able to do in his biography of St. Catherine; ibid. pt. 1, ch. 2 fn 1:

“The virtues and graces of the penitent are not matters for the seal [of Confession], provided they are not manifested in order more clearly to declare the sins themselves, e.g., the gravity of ingratitude towards God*.” (Emphasis in original). (Jone, Moral Theology, no. 618, Imprimatur 1961; TAN reprint 1993).—Publisher, 2003.

* ∵ the more graces one has, the greater his ingratitude could be