Our philosophy is to focus on building community and not aggregating data. This means that while we decline offers to import ‘userless’ data generated elsewhere, we make exceptions if a person wants to join the iNaturalist community and would like help migrating their observations made elsewhere to iNaturalist.
I should note this isn’t always possible/practical. Mushroom Observer has great API’s and we’ve made a nice tool that allows people to import their content from there https://www.inaturalist.org/observations/moimport
For other sites like Observado which don’t have well developed accessible API’s, in the past we’ve help a handful of individual users who contacted us migrate their content by sending us CSV exports etc but this has become too staff intensive for us to sustain, so we’ve started declining requests like these if the site in question doesn’t have well developed accessible APIs.
In three cases we helped orchestrate data migration with groups of people joining from other platforms, you mention the South African migration from iSpot and when the formerly independent NatureWatchNZ joined the iNaturalist network. We also did this with formerly independent Biodiversity4all - now the Portugal iNaturalist Network node. But these groups were still made up of individual users consenting to to have their individual content migrated to their iNat accounts.
The one exception to this philosophy is Questagame which is currently posting observations generated elsewhere to a single group account. This is a temporary situation resulting from a misunderstanding of how Questagame was allowing users to join iNat and post to iNat through their app that we discovered wasn’t line with our policies. Questagame is currently bringing that functionality in line with our original expectations at which time they’ll discontinue posting to the group account.
Hope this helps,