iCloud shared calendar events have vanished?

So we had a shared iCoud calendar 'A' which was set up by Bob.

Bob was going to leave the project so we set up calendar 'B' meaning we could invite other people to the calendar rather than Bob being in control.

After some difficulties I was able to copy all the events from calendar A on to calendar B.

All was working fine.

Then Bob removed calendar A from his phone etc. Then i get a message that "someone has updated 53 events in calendar B" - what this means is that all events have been deleted - and are nowhere to be found.

How on earth can I get this data back? The calendars have been shared across 4/5 people, all using iCloud. Surely somewhere, somehow there is a way of getting this calendar data back??! Please...

Thanks.

PS everyone on the share has been using iPhones and macbooks to access the calendars.