It has been bad lately. I don't have direct experience with multiples in the same design being off in sizing, but I am noticing that styles that would consistently fit me in one size for years (say an a-line dress) now may be one size up or down from my "usual."
The worst experiences I have had lately, though, involve mislabeled items! The Zoe coat I ordered in an XS was MASSIVE. Comical, really. The label said XS, the packaging said XS, and since I was actually concerned that it would come and be a bit tight, I was expecting that I would return because it was too small. Turns out it was an XL parading as an XS. I returned it, obviously, and wrote in MASSIVE letters, "DO NOT ALLOW THIS BACK IN THE STOCK." This is the second time in as many years this has happened.
I think it is at the factory level, honestly. They have such tight margins with fabric that one size 12 in a sweater will be almost a size smaller than another 12 in the same color. I read about how companies manufacture clothing, and it basically depends on where on the fabric bolt the item is cut and how precise the sewer is who is sewing up the seams and hems. Higher end items are cut from the fabric to suit the garment, not to suit the cost/profit margin of the fabric, and they are also sewn with more care. More wasted fabric/more time on the machines equal more expensive clothing.
Though Boden is expensive, for them to manufacture clothing to the precise requirements they used to have and we all used to expect, it would likely cost so much more. Sad state, really.
Big fan of Boden, but I am definitely buying a whole lot less and returning more than I used to...
Will say that compared to many US retailers, though, Boden is like a shining star of quality control. It's horrible over here.