The phrase "additional matter" is correct and usable in written English.
It can be used when referring to extra information or topics that are relevant to a discussion or document.
Example: "In the meeting, we will also address some additional matter that has come to our attention."
Alternatives: "further issues" or "extra topics".
But there's an additional matter.
§ 501.723 Prehearing disclosures; methods to discover additional matter.
Once having satisfied the requirements of subsection (1), any additional matter must fall in subsection (2).
The present volume contains the substance of these papers re-cast, with additional matter, and with a greatly improved terminology.
Volume Three: Manuscripts, Mellon MS 12. Ramon Lull, A Collection of Alchemical Texts Attributed to Lull, With Some Additional Matter.
Manuscript on paper of a collection of pseudo-Lullian alchemical writings, translated from the French and Catalan originals, with a little additional matter.
The large team consisted of all small team members with additional subject matter experts, a program manager and a representative from the NCI.
Additional subject matter experts in the network biology, COPD, lung biology, and biological processes represented by the networks were invited to participate in the discussions and contribute their expert feedback independent from the network-building experts.
The limited powers constitutionally granted to the regions have been extended by the national legislature through its devolution of additional matters to the purview of regional legislatures.
"Job loss, or the potential for job loss, leads to feelings of economic insecurity," Dr. Mather said, with implications for additional matters like the timing of divorce and marriage.
(iii) The Trial Chamber may, in the exercise of its discretion, permit enquiry into additional matters.
