How long is the training to get a Boeing 777 rating if one has a 737-200 rating? I was wondering if anyone knows how long the training for a 777 takes if one already holds a 737-200 rating.
I've looked it up online and didn't find an adequate answer.
According to this site, the course for 777 PIC initial certification takes 21 days (48 h) and the course for 777 PIC recurrent certification takes 4 days (16 h), but there's no mention of anything regarding previous ratings.
Here, someone says they think that to go from the 737NG to the 777 would only take 3/4 sim sessions, and someone else says that the course to go from 737NG to 777 is shorter than the course to go from 737-200 to 777. 

Does anyone know how many days the "conversion" course would take? 

Am I correct to assume one doesn't have to take the full 777 initial certification course if one holds a current 737-200 rating?

And what if the 737-200 rating is no longer valid... does one have to take the full 777 initial certification course?

Thanks a lot
A flight school can offer an "abbreviated type rating course" which takes into account skills from previous type ratings, assuming you have flown an adequate number of flight hours on those ratings.

Boeing also offers a shortened type rating course, details are halfway down their page. To answer your question, Boeing claims 13-15 days for their training and requires 1,000 hours of experience, but it does not depend on a specific rating. There is an even shorter 777-787 conversion as well, that requires a 777 rating.

I think their assumption is that they can skip a lot of basic handling, CRM, checklist type training and focus on the technical aspects. A training provider with the proper approvals could offer a similar class.

Also, for reference, there is the Airbus A320-A330-A340-A380 conversion training which uses the proprietary term "cross crew qualification", and takes less than 2 weeks versus 6 for a full rating. This is done under a EASA approved syllabus, which allows you to do it at any qualified school. Here the requirements are 150 FH on the appropriate Airbus type, and 3 months of experience.