Maybe they get wiped off at start of new season rather than end of old or maybe you got lucky? I know I've been told they get wiped off, at least since they introduced the loyalty points via the ticket booking website anyway.
A couple of years back on the last game of the season I was refused to use my points as it was classed end of the season and no longer valid. (I think it was the last year they had a lady manager (Sarah?) running the shop) She wouldn't even check for me.
Now the workers are more willing to check and allow you to use the points until they are electronically removed. (probably end of may?)
Still need to be more clear about the deadline.