Approved in principle means that everything about the application is good enough for the person to be granted the visa. It isn't described as approved till the person has gone through the final formality of submitting the passport so the visa label can be stuck in.
For the CO to have described your husband's case as "approved in principle", I would think the second-person check must already have been done. COs aren't supposed to tell an applicant their recommendation for the outcome of the application until after the 2pc has been done, for the obvious reason that if the the 2pc official finds any mistake, what the CO thinks about the outcome could be wrong.
Your husband will get an email or letter with instructions - it can be either.