Some chromatic mediants (in the key of C maj, E major or A major for instance), as well as other chromatic chords that cannot be substituted by a secondary dominant (in the key of C, A-flat minor, D-flat minor, etc).
For chromatic mediants I tend not to use secondary chord notation when not resolving to its respective root (i.e, for E major in the key of C, I will search for “III” as opposed to “V/vi” if it doesn’t resolve to Am, the latter works but the former doesn’t). This is admittedly a minor issue, but it’s a bit inconsistent since I have several projects with chords notated this way but cannot add them. Furthermore it makes the aforementioned chromatic chords unusable and only accessible in the projects I’ve used them in.
Using Waterfox G4.1.2 (fork of Firefox 91, should be identical internally). Thanks in advance.