Hello, so sorry for the late reply.
I sent emails to several colleges, and the consensus was that Oxford acknowledge that CAGs/TAGs are a stopgap, and not equal to official examinations. Additionally, if any candidate with CAGs (or results from other alternative arrangements) opts to later sit formal examinations, they will not be disadvantaged in relation to their peers (i.e. they will not be regarded any differently).
However, the proviso was that any assessment beyond the first A Level sitting would be perceived as a retake, and in that case, the applicant would certainly be disadvantaged (failing mitigating circumstances etc). In short, don't retake if you have already sat your A Levels proper at least once, and you should be fine.
Furthermore, Oxford obviously disapprove of multiple gap years (assuming the sole purpose is sitting those assessments) for more or less the same reasons. Therefore, if one were to take longer than a year out, it would have to be justified by providing evidence of other productive activities during that time.