Yes, but the only real recourse is to stay the proceedings if it takes too long to get to trial - which I'm sure no one looking for "justice" wants. If the disclosure is known to exist, the court can order that it be provided by x date.But should it be normal? I mean I know what you said explaining and that makes sense, but really... there should/must be a better way? If disclosure is an issue, can't the judge rattle some cages at least?
The tricky thing is that there can be scraps over the complainant's counselling or medical records (third party records which the issue of whether they have to be disclosed or not has seen much judicial ink spilled over). You can also have complainants indicating that person x y or z was present for something, or that other people gave statements to whoever BB was working for, and those statements have either gone missing or the employer is saying FU get a warrant because they're worried about potential civil ramifications down the road.
It used to be that you could set the matter for a preliminary hearing and use it as a tool to flesh out what additional evidence or witnesses needed to be located prior to trial. But - thanks JWR - the feds have mostly deleted the preliminary inquiry from the criminal code. One of the consequences that those of us who run trials - not JWR - predicted was that it would cause disclosure issues.
You're also talking about tracking down witnesses from decades ago. The main complainant may want this dug up but the others may not. The police may genuinely be having trouble getting statements, but as long as they're working on that I wouldn't feel comfortable setting trial dates, making admissions, deciding which witnesses would be necessary and what the strategy would be at trial, etc.
To defend someone well you have to understand that it's a 3D game of chess at all times, and one move or development can change the approach to the entire board. They'll be looking to put him in jail if he's found guilty - he's entitled to know the case against him so that he can mount a defense if he so chooses...