Flight Crew can operate a maximum of 100 block hours in 28 days and a maximum of 900 block hours in 12 consecutive months, RYR may have a slight amendment to this but it's a maximum of 900 hours per year.
There are also regulations regarding duty hours, not block hours, in seven, fourteen etc. days, I can't even recall which operator I was working for when we were allowed to decide which day of the week our seven days etc. period(s) would commence on allowing us to bust the 'within seven etc. days limits'.
As I posted above I also recall variations on the 900 block hours in 12 months, that operators could variate this to work to their advantage.
But all is as per the operator's Operation Manual which is approved by their regulating authority, in this case I presume the Irish CAA, not JAA.
If the rules are there to be abused then they shall surely be abused, it's not the fault of the operator, if anybody's fault then the fault of the regulting authority that approved any abuse.