It is well known that Thomas devoted considerable time and effort to deepen his knowledge of patristic sources, as can be exemplified by his composition in the early 1260’s of what is known as the Catena aurea on the Gospels.
Recent studies have established that Thomas’ Catena aurea is not merely a compilation of patristic texts but an extensive reworking and reordering of existing sources as well as sources for which he actively searched and of which he had Latin translations made.
Given that the standard Marietti edition contains many textual deficiencies and lacks an identification of the sources, for some years now, an edition is underway which aims to remedy these deficiencies.
Under the direction of Martin Morard and Carmelo Conticello of the CNRS in Paris, an electronic edition of the Catena aurea is being prepared (or as the full title has it: Thomae de Aquino Catena aurea. Editio scientifica electronica, fontibus repertis textuque emendato, éd. Giuseppe Conticello, Martin Morard, coll. Fabio Gibiino et alii).
The project has a most informative website with information on the ratio of the electronic edition, secondary literature, a survey of printed editions, concrete examples of how Thomas went about in composing the Catena, etc.
But most importantly, perhaps, for each Gospel there is a PDF-file of the text with the most up to date version of the text and the identification of the sources so far.
Here is the website: https://big.hypotheses.org/catena-aurea.