OK: to the heart of the issue... Shimano's 6200 derailleur series predates their all-in foray into indexed shifting, which occurred after the expiry of the Suntour derailleur patent (1984).

Note that this rear derailleur does not benefit from the slant parallelogram, which is the heart of the Suntour patent. The slant allows the derailleur upper jockey wheel to better track the profile of the cogset, which is critical for reliable crisp shifting, both in indexing and friction.

Prior to the patent expiry, Shimano made drop-parallelogram derailleurs that superficially looked like the superior Suntour product, but without the slant in the cage, which would have violated the patent. Then they touted them as 'drop pantograph' or some such marketing gobbledygook. This cheesy marketing move resulted in Shimano's derailleurs actually increasing in weight without any of the benefits of the Suntour design.

So to summarize, the Shimano 620X series of derailleurs are NOT SIS compatible, and simply do not shift as well as Shimano's later offerings. I don't know what the cable pull actuation ratio of these derailleurs is, but if they index with any shifters, it will be pure coincidence. But again, they have a major design deficiency due to they could not use the Suntour design.

The instant the patent expired in 1984, Shimano went full-in on indexing, and have been since.