No, I don't mean forge:ores/iron - I see that it was a deliberate decision.

Pyrite and Sulphur (block) don't have forge:ores/sulfur and forge:ores/sulphur.

Lignite doesn't have forge:ores/coal.

Graphite has forge:ores/graphite instead of forge:ores/coal.

Stibnite has forge:ores/stibnite instead of forge:ores/antimony.

Calcite, Anhydrite and Gypsum don't have forge:ores/calcium, despite anhydrite (which is just dry gypsum, really) having the tooltip of being a source of calcium.

The platinum group blocks, Bastnasite variants, Monazite variants, Samarskite and Thortveitite aren't tagged with the elements they are ores of; though I see how it could lead to other mods misapplying them.

On a "it would be nice if ..." note, there are a few ores which can be sources of multiple elements - like ilmenite for iron and titanium - and it would be nice if they were tagged with all of them.

First, sorry for getting back to this issue so late.
I remembered why I did not add multiple tags on one ore.
Imagine a block has 2 tags : forge:ores/titanium and forge:ores/iron. No problem so far. Imagine now you have a mod that adds a crusher machine with generic recipes using tags for its input. What will happen if you insert the block into the crusher ? Will it produce crushed iron or crushed titanium ? I do not know.
Adding multiple tags could produce unexpected behaviour so I will not add more.

These are the changes related to tags I made so far :

fixed chromite tag (chromium)
fixed stibnite tag (antimony)
added calcium tag (calcite, gypsum, anhydrite)
added lignite, graphite and jet to minecraft and forge coal tags

Sulphur block drops sulphur dust, so I decided to tag the latter as forge:ores/sulphur and also as sulfur in case mod developpers use that spelling (most likely).
There is two recipes to get sulphur dust from pyrite. One using a crafting table, when the stone age option is disabled. When you play with that option, you can get sulphur dust by putting pyrite into the refiner.
I do not really remember why I did not tag lignite as coal 🤔, therefore I am adding it to all coal tags, as well as graphite and jet. I am still keeping a graphite tag, since it can be useful for other mod developpers.
I completely forgot to create a calcium tag ! I will fix that.

Regarding platinum-group metals blocks and rare-earth elements blocks, I chose to tag their drops (platinum, palladium, ...) or refinement products (samarium, neodymium, ...). I thought it made more sense than registering multiple tags for the blocks. What do you think ?

Your last suggestion is interesting. I will take some time to think about new tags and add them.

Thank you for taking the time to report those few inconsistencies and giving suggestions.