I recommend contacting to confirm. You are correct, the tour operators can only purchase tickets for the Colosseum 30 days in advance, even if you purchased the tour months ago.
We are visiting Rome in a few weeks. I called my tour operator (not ItalyTours) yesterday and they confirmed that they were able to secure tickets for the Colosseum, but the time had changed by 45 minutes because those were the only time slots available. My Vatican tour time did not change.
I can only imagine how busy Rome is going to be. I keep reading about the massive influx of tourism they are seeing this year.