[Koha] biblio.datecreated and biblio.timestamp created but not displayed

hi, When i create a record, biblio.datecreated and biblio.timestamp (099$c 099$d) are well created in the database but not displayed in the marc file. All seems to be ok but we have to add manually the date. I think it's a question of xsl but, in this case, which file can i modify? Best regards, samuel