Michael,
Yes, inferred dates from things like those CIA alpha-numeric codes are allowed to be bracketed. In the majority of cases you don't even need the question mark, the square brackets sort of imply that it is also questionable.
What goes in the fixed fields are only the dates, no other punctuation marks.
What goes in the call numbers are only the dates, though in older records created using prior older cataloging standards such as the original AACR or even first edition of AACR2 you will see some libraries did things like use a dash for the last digit or a
question mark. I do not know for sure but I think that was local practice that should not have been in the master record, though it is possible too under older ISBD standards that this was acceptable.
Paige
When cataloging resources that lack explicitly stated info (e.g., statement of authority, date of publication), my understanding is that one can record inferred info in square brackets. So in the classic case of CIA maps--which typically imply
through a somewhat opaque alphanumeric code when the maps were created--the 264$c might look like this:
[2018?]
But in that case, what about the 008 and the 050/090 fields? Is it equally permissible to put "[2018?]" into those fields? I've seen plenty of CIA maps, but I'm not sure I've ever seen one with a "?" in the call number!
Thanks.
Michael