Interesting! All of those things make sense, and combining a bunch of incentives and gamification elements like this is probably the way to super-charge completion.
On the contrary, I am a bit skeptical personally about the long-term effects of adding gamification to everything we do. In the end, intrinsic motivation is the strongest force, and I worry (mostly on a personal level) that so much pressure on external motivating factors will make us immune eventually.
In Peergrade, we had a small amount of built-in gamification like this. We would show you how much feedback you had provided compared to the class average. This led to fairly significant improvements in both feedback amounts and quality.
You are using social accountability, be it online or in-person (office setting), to improve the completion rate. I am sure they have worked well for the clients you work with. Here are the few ways I have tried for corporate clients and have seen the completion rate increase in most cases
1. The candidate has to pay a high entry fee (for example USD 1000) and whatever percentage of the course they complete beyond the minimum 60%, they get that percentage of their fee refunded. So if someone finishes the entire course, the course is free for him and if someone does only half or less of the course they pay the full fee. The client then donates the money on the candidate's behalf to a partner NGO.
2. Another is a reward at every level. I don't have enough evidence to say these words, as I tried only once.
3. Course completion is tied to performance metrics but it has to be done with care because the goal is learning rather than a certificate.
4. Displaying % completed for the entire cohort (which can have side effects but is a good motivation device and can contribute towards social accountability.
I did these experiments by combining different tools but my case isn't representative of anything in the industry. So I must repeat take everything I say with a kilo of salt.