Spookily enough I am also someone in cam - it's the Cofco delivery, as you seem to have worked out! I guess it's just laziness in that I usually get home aer my late shift on a Tuesday and realise I've forgotten, yet again, to contact them with my preferences off the list. We certainly do a lot of vegetable soup.
JumpJockey you sound like you could be my neighbour
The mushrooms - in our case you can also alter / fix your base items so I rarely had the mushrooms, just double carrots or potatoes instead. I do express preferences and they tend to work for me but I time it so I do the weekly shop on the evening after the box arrives so I can re-jig my planning somewhat. I do also top up my box from the market to give a bit of extra flexibility.
You might want to look around for alternative suppliers, some are better than others in 'sticking' to your preferences, and also in the options you get to communicate with them - I send a weekly email specifying my 5 pieces from the list on their website on top of the fixed base items. If I don't, I just get a selection plus base which is also fine and sometimes makes life that little bit more interesting . But do speak to them I'm sure they WANT you to be happy rather than go elsewhere.
I also have some flexible dishes in my planning so that I can adjust - Stew is one, obviously, and stir-fry another, and I frequently plan a main (say sausages or chops) and then put any given veg with it. Pasta and sauce, that's another really flexible dish - nearly any veg makes it into my sauce, including brussels sprouts, cooked kohlrabi (great in cheese sauce) or roasted butternut squash.
I think the answer may be to rely on the veg box for half your intake. So if you plan to have potatoes and 2-3 veg for Sunday lunch, say with a big chicken, and make a big vegetable soup as well for other times during the week, and a large pasta primavera each week, it won't really matter what vegetables you have as it can be flexible according to what arrives. Then you can top up with other vegetables from the market for specific recipes. That way you eat a lot of veg but also are able to plan IYSWIM.
That having been said, it can be very helpful to communicate with suppliers about things like random mushrooms and inability to plan, as they may be able to send you something closer to what you want, rather than lose your order altogether.
At the moment we get a veg box delivered which is sourced from local farms, and I really like the idea of supporting local producers. But, it makes meal planning really hard. We get potatoes, carrots and onions every week, plus about 5 mushrooms (!) and then assorted other stuff. They have a listing of what you'll get a selection from, eg about 8 seasonal items of which you get 5. You can express a preference but unless I do this every week, and then plan, and then they still have enough of what we've asked for, it's very hard to plan anything. Eg the list says butternut squash and cabbage, I plan for those and buy other ingredients, we then get kohlrabi and a green pepper.
Are there any brilliant ways to get round this, apart from doing your meal plan the day the box arrives and then going shopping the next day? (ours comes on wednesday so not vastly convenient!) we're more pasta and sauce people than potatoes and meat, so really I'm thinking of cancelling it altogether and getting veg every few days from the market, but would like to be persuaded not to if it's possible to plan better!