I received a response to my email of 25 Jan (post email issue being known) today which was chasing up a response to an email of 15 December (pre email issue being known).

Some points that may be relevant to others:

1. If you are still waiting on TR Sentinel Prime then you may need to get a refund as PC are worried that their "supplier has not delivered the required backorders for several months now, and we are losing faith on our end to promise we can supply." I am personally willing to wait until they know for sure that they won't get the stock.
2. Liokaiser should be shipping out soon.
3. MP-32 Masterpiece Optimus Primal, TR Alpha Trion, MP-33 Inferno and Legends LG-34 Mindwipe should be shipping out mid to late Feb.

They apologised profusely for the delay in responding and advised they will provide me with a further update in a week.

Overall given the huge number of emails they are trying to catch up on, and the fact that I am in no rush to receive any, I don't mind the wait so long as they ultimately arrive. I should note that PC have never failed to deliver on a purchase I have made (and I have made a lot!).