Periodical editions are the easiest to capture. They have most often been reported or reprinted. Journals, bulletins, and other periodicals also tend to reflect the work of groups, and to show the aggregation of information and material (as in KHRONIKA TEKUSHCHIKH SOBYTII and SUMMA). Thus, they provide a general survey of trends in a system that is slippery, because unfixed.
Why periodical editions
Periodical editions are the easiest to capture. They have most often been reported or reprinted. Journals, bulletins, and other periodicals also tend to reflect the work of groups, and to show the aggregation of information and material (as in KHRONIKA TEKUSHCHIKH SOBYTII and SUMMA). Thus, they provide a general survey of trends in a system that is slippery, because unfixed.
But...
But isn't it misleading to call these periodicals? Did they really appear with any regularity?