Imvho it's Sixth daughter.
But I've seen it as the age, which to me becomes difficult to read in some circumstances. And I guess those MNers who see it as age rather than birth order, also get baffled in some circumstances?
Do you wish MN could agree on a standardised standardised format?
Blatantly misusing The AIBU voting facility, may I ask which you prefer?
Yabu - the number should denote birth order.
Yanbu the number should denote age.