Help identifying makers and age.

Hi, first off I love this site. I love looking at all the old pieces! I have several pieces I have been holding on to hoping I can find more information about them but hopefully htere is someone here with more knowledge than me ......... I am still learning ! The first of these is the silver colored brooch 2 1/4" long . It isn't marked other than plat and 14 K. No maker? I would love to know the age and maker if anyone knows.
The next is the round brooch 3/4" diameter. The hallmark has a diamond shape with either a backwards "R" or upside down one depending on how you are looking at. It is also marked 10 k. The last one is a bar brooch 2" long and it looks like it is a 9 C DO. It tested 10'k. The DO could be Dorsons but I can't find proof that he did anything other than gold filled jewelry.
I believe the two gold colored ones are older. I read somewhere that if the pin extends farther than the clasp that it is an indicator that it is from the 1800's. Anyone else think that is correct? Thanks for any and all advice !