@AlaskaDave I agree with you that the link road shouldn’t have main road’s ref tagged as its ref. The ref=* tag is only applicable for the link road if it has its own ref that is distinct from the main road’s ref.
As you mentioned, I also have found some of the link road tagged with ref=* which is the main road’s ref. This seems to be a misused of the tag to tag the link road with the destination road’s ref. In this case, destination:ref=* is the appropriate tag to tell the user which road the road leads to. This tag, however, is not required for most of the link road, especially if there is no signage. If the link road lacks the name and ref tags, the routing engine should be able to inform the user with the main road’s ref. AFAIK, at least OSMAnd is capable of doing this.