As Mark says in the entry, we have most of the data. I'd say 'all' of the data, but I'm not 100% certain, although it's looking pretty likely.

We aren't going to put the whole bug database into the new tracker automatically, because of a combination of the data being there but not easily parsed and thus needing human intervention, and the advantages of a fresh start in not having to individually evaluate older items for "is this still applicable and is this bug still happening", but we have it.