I have no direct knowledge but: SSI could be an acronym for "Società Speleologica Italiana". In Italy we have a national registry and many regional registries (with different codes)
https://speleo.it/catastogrotte/wish

cave:ref:it:SSI=* these codes are not SSI but are regional codes of Veneto (FSV "Federazione Speleologica Veneta")
cave:ref:it:CSL="2006" should be cave:ref:it:SSI="LO2006"

these nodes seem like simple tests
