@twr61 In principle your suggestion makes a lot of sense. In practice I think the References would be hard to maintain.
Consider the situation where two taxa are merged, both of which have different pre-existing sets of synonyms with references. When they are merged, the old synonym references may or may not still be appropriate, because the newly accepted name may or may not have been accepted in some of the old synonym references – if that makes sense.
For some synonyms the correct reference may become the source reference for the new merge. A curator would need to review each prior synonym and decide which reference is appropriate for the newly merged taxon. This could greatly slow down taxonomic curation – which I realize might be a desirable outcome for some But the workload is so vast that I would really hate to see that happen
It’s possible that there could be an automated solution for this scenario – synonyms already associated with the newly accepted taxon would keep their existing references, and synonyms associated with incoming non-accepted taxa would automatically be give the source reference associated with the merge. But I have to imagine the potential scenarios are probably more complex than this, so any potential automation would really need to be thought through first.
@rfoster A preference for secondary references could be stated in the curator guidelines, but I think there would still need to be allowance for cases where only a primary reference is available or appropriate.