θˈiːsən ˈɔːlsoʊ pˈʌblɪʃt "ðə tˈeɪnlɔːɹn ˈɑːɹkaɪvz", ɐ bˌɪblɪˈɑːɡɹəfi ʌv mˈaɪkəl mˈʊɹkɑːk, ænd hɐz mˌeɪd mˈɛni kˌɑːntɹɪbjˈuːʃənz tə bˌɪblɪəɡɹˈæfɪk ɹˈɛfɹəns wˈɜːks, mˌæɡɐzˈiːnz, ænd pɹˈaɪs ɡˈaɪdz, æz wˈɛl æz pɹədˈuːsɪŋ sˈɛvɹəl hˈʌndɹɪd bˈʊk kˈæɾɐlˌɑːɡz.
Thiessen also published "The Tanelorn Archives", a bibliography of Michael Moorcock, and has made many contributions to bibliographic reference works, magazines, and price guides, as well as producing several hundred book catalogs.