A full M&A process should take nine or more months; it is quite possible that there will be contact with seriously interested buyers lasting six months.  A demanding forecast will help push interested buyers to give their best offers, but what should you do if you start to miss your forecast numbers during that time?  

Doing nothing until after offers have come in is risky.  Any bad news is likely to result in a reduced offer; it will certainly reduce your negotiating strength; it may threaten the deal.  So, make certain that interested buyers have the most accurate, up-to-date numbers just before they make their offers.  Perhaps let them know that you want to give them a trading update immediately before they make an offer.  The buyer is trying to persuade you to accept their offer, so they are much more likely to look positively on any explanation.  Once the offer has been made, it is difficult for the buyer to respond in any way other than to suggest a downward revision.  

Should interested buyers be told sooner?  If the fluctuation is part of the normal variation and it does not lessen the likelihood of the longer term projections, then why introduce the thought of a problem when there may not be one.  If the current performance makes the forecast seem incredible, then you would be best to declare it rather than have the interested buyers find out later and think that you have been naive or worse.  Most companies will report on progress every quarter, so use the next quarter boundary as a chance to give an operational performance update and revised forecast.  Take the opportunity to also give some good news and a restatement of the longer term potential of the business as supported by the new forecast.