The ones on the left might have been done by a shoddy roofer, and the ones on the right by a better roofer. I don't recall any national code changes around that time that would affect roofing. ASCE's change to ultimate wind speeds wouldn't have any real effect once ultimate speeds were converted to working stress speeds, just more steps when using working stress design. Did Florida have some amendments?
Agreed...And 2-4 yrs is about 10% of a shingles life so there is bound to be some degradation there.....