Hi Johnnie.
Reference your (somewhat disparaging) comments about the older Western guys in Subic with their 'Oriental' much younger companions: These girls are either 'proper' girlfriends or local bargirls (prostitutes). Just study the behaviour to work out the relationship.
I sometimes was accompanied by my Filipina teenage step-daughter (or one or all of my other children) when in Subic. People sometimes jumped to conclusions when she and I were shopping for groceries there or in Angeles.
The girls arriving with their luggage may simply have been brought through from Angeles or Manila to accompany their 'customer' or boyfriend on holiday.
I very much doubt that the girl you referred to as 'under-age' in fact was (a very serious matter). As you know, Filipinas can look extremely young to our eyes, even though they probably are over 18 years of age, and indeed have to be to legally work in the girlie bars there.