1) 1-month-old, in juvenile plumage. brown underside. 14/11/14
2) 3-month-old, started to moult. 20/1/15
3) 6-month-old, in moult, central tail feathers half grown. 2/4/15
4) 7-month-old, in new 1st adult plumage. New underside feather were pale olive-ish yellow. 18/5/15
I still have to photo this budgie about this week as I made a mistake of not switched the flashing light in my phone, off. Hence too pale colours in last photo (18/5/15).
I'll send better photos here when I am able to.
Hope this helps you since you were been puzzled about what adult plumage look like for SF YF2 DF spangle budgie.
Underside= breast, vent, under tail coverts, belly.