Why didn't they tell me I didn't need to be on time for work?

Tuesday of this week we had  a meeting after school. Most of our meeting was about where we are with preparing for the SACS accreditation visit next year, but there was a little bit on the end where the principal let everyone know that the following day (Wednesday) those who had over 20 lates would have a note in their cubby and would need to talk to him. We have a finger scanner that logs us "entrada" or "salida" from the school. Everyone is supposed to have "fingered in" by 7:15. School starts at 7:30. The school record for lates this year was somewhere around 84.
Supposedly the teachers who had over 20 lates had a meeting Tuesday evening and agreed to not sign whatever was going to be presented to them in their meeting with the principal. You could hear teachers around school on Wednesday griping about how unfair this was for  administration  to make their tardiness part of their official record.
It was almost like it was the administration's fault for them being late. I heard bits of one conversation between someone who is never late and someone who had in excess of 70 lates. It went something like this:
Over 70 Lates, 'It is terrible that the administration never warned us about this.'
Never Late: 'You didn't know you were supposed to be at school on time?'
Over 70 Lates: 'Yes, I knew I was supposed to be on time, but I didn't know I would be threatened if I wasn't.'
Never Late: 'Didn't you know the finger machine was keeping a record of when you arrive?"
Over 70 Lates: 'Yes, but I didn't know that after 20 lates they would threaten me.'
Never Late: 'So you thought you could be late as many times as you wanted and there would be no consequences.'
Over 70 Lates: 'Yes, or they would warn me.'
Never Late: 'What was the meeting with the principal about?'
Over 70 Lates: 'Warning me that if I continue being late it could affect my being rehired.'
Never Late: 'Isn't that what you just said you thought they would do?'
Over 70 Lates: ' Yes, but I didn't know they would write anything down.'

Maybe there is some logic in "Over 70 Lates" thinking.  After 35 years in this business, working in 9 different schools as a teacher, I always thought my being punctual for work would be part of my work record. Why didn't somwbody tell me I didn't need to be on time for work?