This is an Excalibur Umbra with a bunch of Resistances from mods:
These are reflected in both the stats list in the modding UI and the synthesis scanner with the Data-Parse Widget.
All working as it should be.
This is Arda Mutagen:
It claims to add the resistances from Proto Shields. That should be 50% resistance to Puncture, Heat and Corrosive, if it works. Here is a Panzer Vulpaphyla with Arda Mutagen:
No such resistances appear. Testing if they function but are not reflected in the UI would be impractical as a player, and given the example with a Warframe above makes it seem unlikely.
To top it all off, here's my latest project: a Panzer Vulpaphyla with every Mutagen and Antigen, which should grant 62.5% resistance to Slash, 50% resistance to Puncture, Heat, Corrosive, Magnetic, Electric and Gas, and 25% resistance to Impact and Toxin:
Once again, no resistances in the UI. According to comments on the wiki, this issue has been around since Vulpaphylas and Predasites were added to the game in Heart of Deimos. The resistances have never worked.
It took a lot of work to make this Panzer, having the gameplay advantages of doing so that were advertised in the descriptions of the Mutagens would be appreciated.