The bad news is that there are no footnotes in the book. They were originally included in the English version which was to be published by the Academic Publishers of Prague but it never appeared. Svitak died a year later. He was a scholar of considerable reputation, author of many books, etc., so I do not doubt he did not invent this - but not knowing his source, it is not certain whether the information had not come from one of the standard VMS books (living in California at the time of writing, he had easy access to those books/articles).
The tile of Svitak's book is _Malostranska Sapfo_, Praha 1994.