I cannot state specific knowledge, but a few thoughts. I do not know which directories you are looking at, but base my comments on those I have used in my researches.
One clue would be the frequency of publication. Also there are often ammendments to be found, usually at the start of the directory, or a list of changes in some instances since the last edition. Trade entries, especially advertisers are the most likely to be up to date, as they generate the income to the publisher. Residential lists are likely to have least priority.
A directory would take agreat deal of work to assemble, there are examples in the publisher's forwords of them bemoaning the extent of the task, so it would be understandable that subsequent issues would be based on the first and ammended as changes became known. Again this would prioritise the trade entries, and would explain out of date information still being retained.
Lists of council officers are often foundand could be compared to other historical references ( every town will have a list of mayors and dates) Other tables and articles would certainly indicate the latest time of ammendment.
In short, I would suggest that unless it is an advertiser, then inclusion, or absence, may well not be contemporaneous with publication. Perhaps others have an opinion.
