Treat as a successive designation (i.e., " ; " in 362) when:

numbering begins again with "1" (or its equivalent) whether or not the old and new numbering are distinguishable

a serial begins with one type of designation ( numeric or chronological only) and changes to the other (numeric -> chronological or chronological -> numeric); the numbering may begin with "1" or with the appropriate number that accounts for the previously published chronological issues

Treat as a note (when important) when:

serial has both numeric and chronological designation and drops one

serial has numeric or chronological designation and adds the other

numeric or chronological designation changes form but does not go back to "1"

See also:

Module 8. Numbering (fields 362/500)