I’m not sure I understand exactly …
Actually it as happening if you are adding or loading new component definition to the DefinitionList with the same name.
(BTW: there is bug in SU2022, related to this, where this “numbering” will not happen )
Do you mean you want to watch when a new definition is added to the list?
If yes, there is an Sketchup::DefinitionsObserver for that purpose.
Or do you want to listen when the instance of specific definition added? Use Sketchup::DefinitionObserver
Or you check the DefinitionList if the definition with the specific name already exist in it and simple you will not create a new or load it again but use the existing.