Well, I've only been a DL for a few months now, so I may not have this completely correct. There are 2 issues with earning rank that you have brought up, participation and achievements. Achievements seem pretty black and white either the parents (or DL for Weblos) sign off or they don't. And it is a matter of do your best.
The bigger issue of interpretation I think is the participation issue. When I went through training, I don't remember this issue being addressed, but in practice in our pack, it is not taken nearly as importantly as the achievements. Some of the boys in our den simply cannot make it to den meetings (they show up for some, but not consistently). Maybe their parents can't make it, maybe they have other committments. But as long as you can see that they are making an effort and not completely blowing off the pack, then I don't think it has been a problem. In that case, it is just a matter of whether they have done all the required Achievements.