There is an abundance of information to be found in the various introductions of the different Mabinogi translations (occasionally titled the Mabinogion, after the erroneous translation error of Lady Charlotte Guest in 1838). As translators and interpreters of their work, the authors/editors of these collections naturally have an interest in establishing the importance and legitimacy of their texts; what they say about the works, the sections included or excluded, or the changes made, all speak to what is important to them and their readers -- and, as such, what is important to manipulate for best effect.
There is a running theme: the desire for the establishment of the antiquity of the work translated. Reading several translations from earliest to latest (Guest 1838, Jones and Jones 1948, Ford 1977, and later Davies 2007), we can see the assumptions made and challenged. Getting into the 20th century, a growing amount of scholarship on the stories of the Mabinogi makes for more in-depth commentary that translators can engage with, and the length of the introductions grows correspondingly. Guest appeals to what authority she had access to (citing Geoffrey of Monmouth, Layamon, Wace, Bede, Albin, and the translators thereof) -- who she sees as, in reproducing historical texts like Nennius's Historia Brittaniae (though this attribution is contested), evidence of the spread of Celtic culture, allowing her to trace origins back to North-West France and further to Celtic Wales, giving rise to her assertion that this is thus the cradle of European romances. She does not appear to consider that their sources might have been flawed, or even that portions could have been wholesale invented. Geoffrey and Bede are certainly known now as unreliable sources of pseudo-history. She also uses toponymy for evidence of antiquity, making the absurd assumption that place names in Wales that refer to legends (e.g. Llyn y Morwynion, Lake of the Maidens) are ancient, stemming from the first settlements of the area (by virtue of the words in the names being ancient, fallen out of use, or forgotten) and thus -- as she says the legends they refer to must predate the names -- the stories in the Mabinogi must be from antiquity. This is clearly an erroneous assumption: places are frequently re-named, by inhabitants or by conquerers, and any of these people may use archaisms or reference mythology in order to reinforce their claim to the land via their supposed association with antiquity. The names could thus be a result of nationalist legitimizing (or other 're-branding' in the same manner as how Saint Petersburg never had any historical connection to its namesake). However, as stated, acknowledging where past scholars' and translators' biases lie enables us to look forward to what adaptations and translators of later works also might seek to change.
Jones and Jones give effusive praise to the writers of the tales of the Mabinogi, setting up an atmosphere of reverence for storytellers that I feel might serve to glorify themselves, self-mythologizing, and thus to further the legitimacy of their own work as well as grant importance to the claimed past. They also lament 'lost heritage' in what they see as portions missing from the corpus (based on their own interpretations of how the stories are mutations on standard mythological stories, and thus where they lack portions that conform to their dominant narrative, they assume there must have been pieces to fill in the blanks), but also espouse pride in what remains (but disparage what they see as unnecessary onomastic additions), clearly displaying their editorial bias and letting we readers know that what theories they state must be critically examined. As of now, Jones and Jones appear to me be part of the tradition of Freud and Jospeh Campbell, trying to unite literature with psychological archetypes and stories (they may have commonalities with Aarne, Thompson, and Uther in the mere categorization of stories, but Jones and Jones do take it further to try and force the tales into an unsuitable mold for which explanations must be made as to why it doesn't perfectly fit). This brute force theorizing reminds me of a text I've wanted to get hold of, 'Theorizing Adaptation' by Kamilla Elliott, which talks about the problematic aspects of adaptations -- I've put an interlibrary loan request in for this. Jones and Jones claim to have produced a critical text (Ford calls it a literal and rigorous text), as opposed to the diplomatic translations they mention having consulted, but their assertions in the introduction reveal there may be subtle tweaks and adaptations to watch out for an examine why they did the things they did.
Ford, in his introduction, outright states that his primary concern is the medieval expression of 'native mythological themes' (and thus omits the Arthurian romances and dream literature included in other editions, but ensuring the 16th century Taliesin texts are present), wanting it to be both accessible (in particular to university students) and true to the feel of the original (e.g. using contemporary 'you' rather than the archaism 'thou,' as the words in the original old Welsh did not have an archaic sense to them). He theorizes that the four 'branches' of the Mabinogi are intended to be collections of thematically and metaphorically related individual tales (thus reducing the supposed confusion of continuity errors), episodes that can be examined in isolate, but all of which can be grouped under his preferred etymology of 'Mabinogi' (Prof. Hamp's etymology of 'collective material pertaining to the god Maponos,' Maponos being the British version of Pryderi's father, Pryderi arguably being one of if not the central figures of the tales). His 'eclectic' theory also draws on other onomastic/etymological explanations (e.g. linking the character Rhiannon to the continental Celtic goddess Epona, via Latin but by means that look to me similar to the back-construction of the proto-Indo-European language -- will explore this later), but also with euhemerist explanations (linking the stories back to central events that generated 'literary reflexes' that then proliferated throughout/alongside the Celtic diaspora, none of which have any historical evidence). Jones and Jones also indicated euhemerist tendencies, and between this and the linguistic-based theories, these translators all seem to epitomize the field of mythological studies, with its strengths and weaknesses. It remains to read the Mabinogi versions all in full, comparing where translations differ, to see if it makes any subtle differences (major differences are evident in what was chosen to be included) in how the text is read and received. This will then, going forward, inform my understanding as I learn about adaptation and translation processes.