Blanket L1

I am an IT manager for the Canadian subsidiary of an American company. I've been told that other managers frequently travel to US offices under a blanket L1 status. I've been with the company for nearly a year & have a couple of questions about travelling to the US under this blanket L1

1 - How does the L1 time limit work under a blanket visa (or is there even a time limit when using a blanket L1)? If i only spend a few days per year in US offices, do those days count towards the 7 year time limit or does the clock start ticking the moment I enter the US under this blanket L1, regardless of how many days I'm actually in the US?

I guess that's the only real question I have. It seems like this 7 year time limit really puts a cap on the number of years a manager can work for this company. My job requires me to travel to US offices, but what happens after 7 years? I have to stay home for a year to reset the clock? Not that I'd necessarily stay at the same job for that length of time, but who knows??

Thanks for any help you guys can provide.

Maybe this document at the Departement of State will help

http://www.state.gov/documents/organization/87229.pdf

It's called an "intermittent" L-1, provided you stay in the US for less than 183 days a year the limit never kicks in, although I'm not sure how it works if you go in under a blanket L-1. However whatever the bureaucracy involved is, it definitely is possible to stay in L-1 status indefinitely if you only go in a few days a year.