We are *obliged
to confess all mortal sins in number *(now many–which may need to be an approximation if one does not know how many -one approximates according to what one does know…10-15x, few x, many x, around once a month for the last 2 years) and *kind (*fornication, masturbation, looking lustfully, murder) and that which changes the kind ( species) such as it was a chalice one stole --or it was your brother you murdered.
Now lets say one has not hidden mortal sins in the past but sought to confess all one knew one had to confess (if one hid such --that is a bigger problem to address with the Priest in confession)
What is one to do if one remembers a mortal sin (grave matter, full knowledge committed with deliberate consent) that one has not confessed? Or that one confessed a mortal sin but forgot to say it was 3x. Well one is obliged to confess it. So that is what one does.
So yes if they were mortal – one confesses them.
Number and kind are not “details” they are part of the confession of mortal sins. Now some may seek to give “unneeded details” – one does not need to give unneeded details of the sin…
Jimmy Akin of CA
jimmyakin.com/2006/09/a_reader_writes_1.html
(Now some readers out there struggle with scruples (scrupulosity) in this area and can start to want to confess all sorts of un-needful things etc etc --they need to have a regular confessor to direct them. And their confessor may need to give them directions that others would not follow --due to their scruples)
Know that Jesus is the Good Shepherd --he loves you and desires to give us true life!
Confession being one way he does such!