Hello, I recently found out that when confessing mortal sins it is necessary to include the number of times it was committed.
Correct. That’s Catholic dogma, affirmed at the Council of Trent in response to the Protestants.
It’s also common for lay Catholics to not be aware of it
as a specific requirement and questions such as yours appear here regularly.
… in the past when I confessed mortal sins I did not include the number.
Your priest however
does know requirements for confession (1), and he is the adjudicator of your confessions. If he is satisfied that you have made a good confession then that’s the end of it.
If you later remember a mortal sin which was innocently forgotten then you should
mention it in the next confession, but it has already been absolved.
Is it necessary for me to mention it again this time with the quantity?
No.
But if it bothers you then just bring it up at the start of your next confession. It should take less than a minute, eg. “Father, in previous confessions I didn’t know that I had to confess the number of mortal sins, but I made the best confession I could at the time”.
Priests are always happy to answer questions within the confessional and are just pleased that you are there.
For future reference, confessing the “number” doesn’t have to be a digit such as “nine”, “Four thousand and seventy seven”. “Lots”, “Two or three times a week”, “a few”, etc.
can all be valid. If not, then the priest will ask.
Just do your best, and remember that it is up to the priest to know the law and you don’t have to second guess him.
(1) For a priest to hear confessions the local Bishop must first give him “faculties”, which ensure that he is properly qualified.