According to Appendix 1, page 229, both are acceptable. Hereabout and whereabout are both on the shortforms list. The paragraph at the top says that an 's' added to any word on the list doesn't change that fact (with the exception of abouts, almosts and hims).
I am not seeing that it is okay to use ... as it does not appear in the Appendix 2 list. I have had a couple of people ask me about it ... and recently had a student ask me because she was told it couldn't be used because it was not on the Appendix 2 list. I guess my confusion lies in why is it ok for hereabouts using the dot 5 contraction and adding contracted abouts ..(adding abs) but I don't see where it is allowed in whereabouts (no apostrophe 's) using the dot 5 "wh" and adding shortfdorm abouts (abs). I apologize if I am confusing you 🙂
I am a bit confused...but here you go. This is what I know.
hereabout and whereabout are initial letter contractions.
According to 10.7.1 these types of contractions can be used wherever the letters they represent occur (unless another rule prohibits that). I can't find any rule that prohibits either of these being used in hereabout or whereabout.
The rule for shortforms says what you noted in the first post above (I'm not going to repost it here).
So I then go to Appendix 1...which deals with shortforms. Look at the list regarding the shortform word 'about' (page 229 of the code). Both hereabout and whereabout are on that list...so both are acceptable.
Now we add the 's'. If you look at the paragraph at the very beginning of Appendix 1 (under "The list") it says that when an 's' or apostrophe 's' is added to any word on the list, use the shortform with the following exceptions...I realize that abouts is one of those exceptions...but it is not the word hereabouts or the word whereabouts...it is the word abouts all by itself (and that's probably because the contractions abs could mean abs [a different word] rather than abouts).
So hereabouts would be (here)(about)s and whereabouts would be (where)(about)s. Since hereabouts is shown as an approved word on page 138, my logic is sound...and would apply to whereabouts in the same manner.