I find those ID charts hoplessly inadequate. They are obviously designed for 'molagists not the general public. Why can't they produce a definitive photo gallery of all the bumblebees with queen, worker and male side by side? A couple of weekends ought to be enough time.
I have lots of the tree bumblebees on my plot that look just the same as Helens plus another one that so far does not fit with any of the charts I've seen. Solid lemon thorax, black body, orange tail.
Unfortunately I've no camera at the moment.