@rjq yes, Tarangire & Manyara Dik-diks are M. thomasi. Those from Longido east to Mkomazi are M. hindei. From Natron west to Serengeti, you have M, cavendishi.
the taxon change forced most former M. kirkii to be M. hindei, which is fine for all those in southeastern Kenya, but not for those in north central TZ. So we're slowly going through them to change them to the correct ID - M. thomasi. The two former subspecies (thomasi & hindei) used to be part of M. kirkii. Those that had already been ID'd down to subspecies level (eg. Madoqua kirkii thomasi), automatically got swapped to M. thomasi. Those that were only ID'd down to species level (M. kirkii) automatically got swapped to M. hindei - I think erroneously.
Either way, the dik-diks from central TZ all the way up to just north of Manyara (but south of Arusha) are all M. thomasi. Those in Serengeti are M. cavendishi, and those from Arusha to Mkomazi are M. hindei.
It's a long, slow process going through all the old records from each area to ensure they now have the correct ID, and often the original posters don't come back to amend their ID's even when tagged and presented with evidence.
the current change in dik-dik taxonomy on iNat is based on the Mammal Diversity Database: https://www.mammaldiversity.org/taxa.html
You can read more about the various (former) subspecies and their biogeography here: https://www.wildsolutions.nl/wp-content/uploads/De-Jong-Butynski-2017-Madoqua-EA.pdf