Can't you wait until the flower is matured enough on the plant to collect the pollen? Why pick the flower so soon?

Many release their pollen long before the petals open, hoov. There are more than you might expect which begin pollinating themselves before the sepals begin to unfurl, making using them as either parent a real chore. You have to experiment to determine which release it when to prevent self pollination (which is much more common than you might think) as well as loss of the pollen before you get to it.

Yes, fully dried anthers can be ground to release any pollen they may contain and it can remain effective enough to produce results. Some roses don't make pollen. Some have deformed anthers which refuse to release it. In really humid conditions (which, from your being in the Philippines, seems as if it may play a role in this issue for you), the "wax" holding the pollen on the anthers may dry like glue, preventing the pollen from being released. Sequoia Nursery ground dried anthers from reluctant parents for many years. Kim

@ hoov
I forgot to state that I actually tried that before to have them self-pollinate and I still get the same results: Dried up anthers with not a speck pollen on the stigmas. I even waited around for hips until the flower dried into a brown wand on the stem.

@Kim
Thank you for that useful information! I'll try that when the next blooms appear. (Hopefully my Center Gold blooms around the same time. I've read that it makes a good seed parent.) And yes, it has been more humid here than normal since it's the wet season right now.The humidity here was probably what kept my roses from releasing their pollen all year.

I see, thanks for the explanation noir and kim. I've been playing around with Agave/Manfreda crosses this year, and found the pollen wasn't appearing on some flowers until the flower was just about spent.