On the unrelated cases, it seems that this case has attracted so much publicity so far that it is pretty inconceivable that anyone with a case against diggory would not be aware of stephen manning, therefore I assume they do not wish to be associated with him. He himself appealed for the unknown person(s) to get in touch with him, ask him yourself.
That's quite an assumption. The reasons someone may or may not tie in their legal case with someone else's are varied and broad. Ditto for discussing your case with a complete stranger, no matter what you may have in common.
As far as personal associations, or not joining his support group, the phrase "do not wish to be associated with him" carries implications far beyond simply not caring to join his support group.
I guess if Mr. Manning can't document the one hundred complaints, you are right to be skeptical of the figure. But there are still quite a few documented complaints against Diggory. Twenty-two people had complaints that they could not resolve and felt forced to take legal action. Mr. Manning may be quite a personality, but it takes more than personality to go to court.
If the court exonerates Diggory, then I'll be convinced of Diggory's honesty. Unfortunately, it looks like we'll have to wait a while.