Another respondant from the Sorbian Institute in Leipzig tells me:
(translation by babelfish.altavista.com)
The name Tetzlaff is westslawischer [West Slavic] origin. It is derived from Teclaw. The name Teclaw is for the first time in the sources as Th(e)sizlaus 1189, a little later to 1229 also than Tezcezslaus (Tìšislav). This word is derived from urslawischen [??] terms tìšiti = gloryand slava = fame, celebration.
So the numbers listed are dates - all that's unclear is the transition date from Tezcezslaus to Teclaw and from Teclaw to Tetzlaff...