If it has been serviced to the manufacturers schedule then it is a full service history.
If any service has been missed it is not a full service history.
Simple really.
Just saying.
It can get a little more complicated. E.g. my R129 SL500 was due 12 monthly services, however the main dealer I took it to advised dropping to 2-yearly because of the very low annual mileage. So it was serviced as advised by MB, but not as per the manufacturer's schedule!