Hello Tiemen. Yes, it's quite possible that someone could be born in one place and baptised in another. That could be the case if the expectant mother went to stay with her mother for the birth, to benefit from the latter's experience. She'd afterwards return to the parish where she was currently living, and the baptism/christening would take place there. (Formal registration of
births only started in 1837, and even then registration of a birth could be made in one place and the baptism/christening in some totally different place - in the case of my immediate family, hundreds of miles apart!)
In the 18th-early 19th cents I'd usually gamble on the birth and baptism happening within a village or two of each other, as might be the case with Harleston and Shelland. But, having looked at John ('Cockeye'??) Carbold's history as given in the Old Bailey proceedings and also the London Gazette
http://www.oldbaileyonline.org/images.jsp?doc=OA175012310011 it might not be quite so easy where he's concerned. For instance, I see that he was apparently 'bred a baker' - but in Yarmouth, Norfolk, which is miles away from Harleston, Suffolk! And maybe it's just awful coincidence, but I see from apprenticeship records on ancestry that another John Carbold was a master baker in Beccles, Suffolk, in the 1720s... So you may have to look far and wide for JC's baptism.
I don't think there's much more I can do to help (especially as I don't live in either Suffolk or Norfolk, much to my regret), but other rootschatters might be able to.
Birtle
Btw (by the way), POB = place of birth. DOB = date of birth. (I use DOBp for baptism/christening)