Okay, let me attempt to clear up a couple of misconceptions.
Anyone who wants info on the finger scan itself can read about it
on Deb's web site.
Hand stamps are not done on different hands depending on the day of the week. They are done on different hands by different parks. Two use the right hand (MK & MGM) and two use the left(AK & EC). It doesn't change. But the stamp they each use changes daily.
There
are black lights set up at the turnstyles. There are also handheld ones that most CM's will use to check for hand stamps. Gate CM's are notoriously lax in checking for handstamps though. It doesn't mean it isn't done but it can hardly be said they do it with any regularity.
The reason for having the hand stamps has nothing to do with the computer system being down. BTW, Disney has two backup systems to the main ATS so the chances of that happening are infintessimal. The hand stamps prove that it was
you who used the ticket that day.
I too have many friends who are WDW CM's. They are experts in their own area. Disney does not share policies and procedures with them that do not affect their own area. Merchandising isn't told when a CRO/WDTC policy changes, food service isn't told when a ticket procedure changes, maintenance isn't told when an office procedure changes, etc etc. Some of the worst WDW information I've personally heard given has come from CM's who attempt to answer questions from guests pertaining to things outside of their area of expertise. They are mostly wonderful people but they aren't always right. Why do you think Tyler keeps cautioning people that if they want reliable tranportation info, ask the folks in the purple pants? Because they know their own department better than any other CM's.
For the OP, if you are using your 10 day when you are at WDW, you only have 21 days from first use to use it entirely or you lose it. The unused days are
not good indefinitely like regular park hoppers.