Should put pollen underneath a microscope w/ a usb attachment (takes easy online photos).

Don Gers comments:
The distinguishing characters of "General Vallejo's Yellow Banksiae" are the larger individual flowers, 4.4 cm (the diameter of a silver dollar), with more petals, about 75 per flower and a longer pedicel, 6.5 cm (the length of a toothpick).
Whereas Rosa Banksiae lutea, the common double yellow Banksiae has about 40 petals per flower with a diameter of 3.3 cm ( the size of a half dollar) and a shorter pedicel length averaging 4.2 cm long.
So what is the origin of this rose? Because"General Vallejo's Yellow Banksiae" looks like the common double yellow, Rosa Banksiae lutea but on a grander scale it could be what's called an amphidiploid. This comes from the union of unreduced male and female gametes resulting in a tetraploid offspring from diploid parents.
Or, as my rose friend Judith Serin suggested, it may be the Banksian rose 'Jaune Serin' larger in flower than the common double yellow. But some early authors also state 'Jaune Serin' flowers are deeper yellow than Rosa Banksiae lutea. However, Gertrude Jekyll in her book, Roses for English Gardens wrote: "....Jaune serin--has larger, paler flowers on longer stems, is decidedly less brilliant in effect...". But perhaps she didn't actually have 'Jaune Serin' but instead had the "General Vallejo's Yellow Banksiae" form.