Those are called ficta. Roughly, these are accidentals that were implied in older music but not notated. The performer would have known to sing or play them. Placing the accidentals above the note in urtext or a critical edition tells us that it was not found in the manuscript or contemporary copy.

If you look up the term, you will find reams on info on the subject.

Sometimes ficta is subjective and interpreters can disagree. Other times, there is no doubt—lute and viol music, for example, may not show an accidental while tablature shows the actual fret being played.

Hello Mike,if you have already received a reply,my apologies,I am never too sure whether to reply directly to th E-mail or through the support

page.

Kind regards

Eric Johnston

Hi Eric,

This is a users' support portal. Rarely will MM Support weigh in — especially on a question like yours which is not support related at all. You asked what they are, not how to create them and I answered as simply as I could. MakeMusic personnel are identified in their signatures on the rare occasions that they weigh in. The rest of us are users like you and cannot be contacted through support. You saw an email from me because I replied to your question and vise versa. A few of us are designated Community Experts only because we answer a lot of questions on these boards but we have no affiliation with MakeMusic at all.

To contact Support directly, use the Submit a request link at the top of the page.

Back to your question. If those accidentals showed up when you didn't intend to create ficta, then that's entirely different—that's not supposed to happen and is a support question. Likewise, if you have a need to create it, this can certainly can be done in Finale (and a few other notation apps—but not Dorico yet) and is a different support question which I and a few others can certainly answer.

So, if you weren't asking about Musica Ficta, what is the real question?

https://makemusic.zendesk.com/hc/en-us/community/posts/215729367-General-Discussion-House-Rules

Hi Eric,

It looks like you have been responding to the email notifications sent out by our system when another posts to a thread that you are copied on. Those responses go to an unmonitored email box so, with forum threads like this, you will want to post directly on the page with a comment so that other users like Mike see your response. 

I hope this helps clarify things for you.