AACR2 21.2C2. Definition of major and minor title changes for serials

21.2C1.
If a major change occurs in the title proper of a serial, make a new entry.
21.2C2. Definition of major and minor title changes for serials
a) Major changes. In general, consider as a major change in a title proper of a serial the addition, deletion, change, or reordering of any of the first five words (the first six words if the title begins with an article) unless the change belongs to one or more of the categories listed in 21.2C2b.
Consider also as a major change the addition, deletion, or change of any word after the first five words (the first six words if the title begins with an article) that changes the meaning of the title or indicates a different subject matter.
Also consider as a major change in title proper a change in a corporate body name given anywhere in the title if it is a different corporate body.

b) Minor changes. In general, consider the following to be a minor change in a title proper of a serial:
i) a difference in the representation of a word or words anywhere in the title (e.g., one spelling vs. another; abbreviated word or sign or symbol vs. spelled-out form; arabic numeral(s) vs. roman numeral(s); numbers or dates vs. spelled-out form; hyphenated words vs. unhyphenated words; one-word compounds vs. two-word compounds, whether hyphenated or not; an acronym or initialism vs. full form; or a change in grammatical form (e.g., singular vs. plural))
ii) the addition, deletion, or change of articles, prepositions, or conjunctions anywhere in the title
iii) a difference involving the name of the same corporate body and elements of its hierarchy or their grammatical connection anywhere in the title (e.g., the addition, deletion, or rearrangement of the name of the same corporate body or the substitution of a variant form)
iv) the addition, deletion, or change of punctuation, including initialisms and letters with separating punctuation vs. those without separating punctuation, anywhere in the title
v) a different order of titles when the title is given in more than one language in the chief source of information, provided that the title chosen as title proper still appears as a parallel title
vi) the addition, deletion, or change of words anywhere in the title that link the title to the numbering
vii) two or more titles proper used on different issues of a serial according to a regular pattern
viii) the addition to, deletion from, or change in the order of words in a list anywhere in the title, provided that there is no significant change in the subject matter
ix) the addition, deletion, or rearrangement anywhere in the title of words that indicate the type of resource such as “magazine,” “journal,” or “newsletter” or their equivalent in other languages.
In case of doubt, consider the change to be a minor change.
As appropriate, give, in the note area (see 12.7B4.2), those changes not considered to constitute a major change in the title proper. Make added entries as instructed in 21.30J1.