From Splunk docs:
Searchable Data Copies: The number of complete searchable copies of the index that the cluster has.
Replicated Data Copies: The number of copies of the index that the cluster has. Each copy must be complete, with no buckets missing.
It shows that the moment you have one replicated data copy which becomes one searchable data copy, this data is searchable.
You can look for more details about the actual number of copies and buckets using this search:
| rest splunk_server_group=dmc_group_cluster_master splunk_server_group=dmc_indexerclustergroup* /services/cluster/master/indexes | fields title, is_searchable, replicated_copies_tracker*, searchable_copies_tracker*, num_buckets, index_size | rename replicated_copies_tracker.*.* as rp**, searchable_copies_tracker.*.* as sb** | eval replicated_data_copies = "" | foreach rp*actual_copies_per_slot [eval replicated_data_copies = replicated_data_copies." ".rp<<MATCHSTR>>actual_copies_per_slot."/".rp<<MATCHSTR>>expected_total_per_slot] | makemv replicated_data_copies | eval searchable_data_copies = "" | foreach sb*actual_copies_per_slot [eval searchable_data_copies = searchable_data_copies." ".sb<<MATCHSTR>>actual_copies_per_slot."/".sb<<MATCHSTR>>expected_total_per_slot] | makemv searchable_data_copies | eval is_searchable = if((is_searchable == 1) or (is_searchable == "1"), "Yes", "No") | eval index_size = round(index_size / 1024 / 1024 / 1024, 2)." GB" | fields title, is_searchable, searchable_data_copies, replicated_data_copies, num_buckets, index_size | search title="***" | search is_searchable="*" | rename title as "Index Name", is_searchable as "Fully Searchable", searchable_data_copies as "Searchable Data Copies", replicated_data_copies as "Replicated Data Copies", num_buckets as Buckets, index_size as "Cumulative Raw Data Size"
