In effect, when it comes to flight, a passenger is a passenger is a passenger. Whether someone checks in on their own who has a reservation on their own, or who is part of a reservation that includes others or anything else ("linking" as you mention which amounts to close to nothing in practice) makes no difference, so your wife can check whenever she wants and check in luggage corresponding to her allowance without issue. You can then check in in your own time and check bags or not, or not come at all for that matter it does not make a difference.

I'm surprised by the mention by someone else that they were able to check in bags for others without them being there using their passport and BP. I don't think this should have been allowed and is clearly a security risk. Apart from anything else, how could you possibly answer the potential standard questions on whether you have packed the bag yourself, whether anyone has given you anything to take etc if the bags are not yours? Beyond it however, I think it's a very bad idea to leave your passport to anyone else for obvious reasons.