How can I tell which Bhutan 1/2 Rupees I have?

I have 4 Bhutan half rupees, that all look pretty much the same to me. The weights range from 5.76 to 5.83, suggesting they are the KM#25, but they're not silver.

The KM#28 is more common, but weighs less. The KM#26 weighs 5.7, but is quite rare, and it would surprise me if all 4 of mine were a rare one. Are there other varieties?

There is a KM#28.1 too which weights 5.85 Grams and is Nickel, http://secure.numismaster.com/ta/Coins.admin?rnd=YVMOWBWZ&;@impl=coins.ui.ucatalog.flat.coin.UiControl_ViewPriceGuideDetail&@prms=4b7261757365436f696e49643d34303337342653656172636849643d33323439383138&@windowId=SEPJC&Ext=login

I will use this old forum chat to clarify the difference of Bhutan KM#26 and KM#28.

I checked many sources, but I did not come to a clear end and I think many collectors identify these coins wrong. Or I miss an information ...
Maybe you help me.

I think the picture in Numista for KM#26 is wrong (I think it is the picture from KM#28).
Why I come to this conclusion? If I read the KM catalogue 2017 in detail, KM#26 should be identical with KM#24 (but Nickel instead of Silver) with the inscreption of the DRAGON-YEAR in the central square.

KM#28 has the TIGER-YEAR in the central square.


Is KM correct or is Numista correct?
And I have never seen the Nickel coin with the DRAGON-YEAR in the central square.

Thanks
Rupert