>> The languages were similar on many points, and there was
>> no science of etymology to pick apart the sound-changes.

> Though it's clear that some of them were recognized and

allowed for when Scandinavian names were borrowed into Old
English, since the proper substitutions were often made.

Good point. <Swegn> is an example of one where the substitution wasn't made, but maybe that had more to do with a sense of incongruity at using the noun <swán> as a name than a failure to recognise the equivalence.