I think that Jan may be also know as Jan z Bystre. Jan z Bustre was a signatory of the Letter of Protest by the Czech Nobles in 1415 about the trial of Jan Huss.
At about that time Oldrich z Boskovic held the estates of Svojanov and Bystre. The coat of arms of Bystre is a Beat and a huntsman and this is the symbol on the seal attached to the letter.
