For sure many Victorian and Edwardian sporrans have those two wide straps on the back, and military horsehair sporrans have done until recently, due to the assumption that a plain leather belt would be worn.

I think it's when chain-straps became more popular that soldering the rings on the back-plate of the cantle became common.

From imagery it seems that around 1900 the chain-straps started getting more popular than leather belts for Evening sporrans, but yes chains are sometimes seen in Victorian times, usually with quite ornate cantles, which presumably had the rings.

It seems clear that the D-adapters were intended for the 20th century sporrans with a leather slot-tab sewn on the back rather than the two wide leather loops.

Sadly the catalogues only show the fronts of the sporrans, and in photos and paintings of men wearing sporrans we can see if it's a chain or a plain belt but we can't see the attachment.