Hi Eric, welcome to the forum!
I’m not sure if I quite understand the type of observation you’re looking for. Can you provide an example? Are you looking for original IDs that were withdrawn, or for cases where the observation has a disagreeing ID that follows the original Abronia ID?
I’d generally recommend using the Identify page. For example all observations that are currently identified as Abronia that need identification will appear here: https://www.inaturalist.org/observations/identify?taxon_id=50255 The Identify page will automatically exclude the ones you have already added IDs to.
There’s also a particular search filter, ident_taxon_id, that you can add directly to the URL. This filter, when used with the lrank as well, can help find observations where one of the IDs is Abronia, but there’s another ID that disagrees with it: https://www.inaturalist.org/observations/identify?ident_taxon_id=50255&lrank=subtribe
More about using the Identify page here: https://www.inaturalist.org/pages/video+tutorials#identify
And more about using search filters in the URL: https://forum.inaturalist.org/t/how-to-use-inaturalists-search-urls-wiki/63