You can't tell too much from this.
You need to know:
- how the classes are nested;
- whether some of the fares (e.g. L and I, or Z) are special fares which are not normally available
- what the airline's normal yield management practice is...
The number "6" probably just means "6 or more". You'll often see 4 or 9 instead. (Another possibility as TwinAisle mentions is that the classes are not nested at all - 12 x 6 = 72, close to a Q400's capacity.)
The one halfway useful idea you can get of how full the flights are is by looking at the lowest booking class with seats available, knowing that it's the lowest classes which will fill up first. The displays of the sort you show will typically show classes from highest to lowest (with some exceptions), so Z is probably the lowest.
If the classes are nested, I would guess the first flight has very few bookings, as the lower classes are still open (it might have 12 people booked, or the L and I classes might just not be available on that flight). The second flight could have as few as 6 seats left - it's really hard to tell without knowing how flyBE nest their booking classes.