EDIT

In SQL Script the Taxon.SourceFk was filled the following way:

• for taxa from ERMS, FauEU and IF it was filled by the according single reference of type "database":
  "ERMS export for PESI", "FaEu_v2.6.1 export for PESI", "IF export for PESI"

• for E+M it was filled by the sec-reference of the PTaxon (also for misapplied names the sensu reference was taken - it always existed due to Not Null constraint)

• for E+M pure names no source was given

If records were merged, the source from the primary record was taken (the one first to be mentioned in Taxon.OriginalDB

All these reference are not really for human readability as the first are partly abbreviated using unknown terms and the sec references in E+M were primarily for rights management less for showing information (they were replaced by the last scrutiny references during import from E+M BM to CDM).

So the question is what they are intended to be used for and if we need them at all.

Until then we export them similar to the above described way, but by using the new sec references for E+M and where ever no sec exists for a taxon (misapplied without sec) using a general "Euro+Med CDM database" like for the first 3.

The real solution of this ticket probably needs to be moved to PESI 2020.