A “deadline” for cooption is a peculiar concept anyway. Whilst it could be a useful admin tool if there are many prospective candidates, what seems more likely is insufficient or no candidates. In this instance, a deadline is pointless since it will have to be extended in perpetuity until a candidate does emerge. Perhaps a better way to approach the issue of cooption is to set a ‘rolling deadline’ similar to that for items for the agenda - eg 7 days prior or whatever is specified locally.
If a candidate submits incomplete info it could be that they are ineligible for consideration or it could be that they are presented for consideration on the basis of what they have provided.
Is it the case that ‘some’ don’t ‘like’ the existing candidate and have sought to make them ineligible whilst they scrabble around trying to seek a more favourable candidate - that would come as no surprise….