I'm not sure of the current policies, but you may not get review credits towards a premium membership for older reviews. If a provider is using reviews as part of her screening process, it is probably only to help her evaluate whether you are respectful, but reviews are not a very good screening tool in my opinion.
Also, take into consideration whether or not these providers have many reviews or not. If they are well reviewed, will your review be adding new or different information? If not, then it isn't worth much to your fellow hobbyist, unless your experience was markedly different from most of the others. Reviews should be for your fellow hobbyist and not as a favor to the providers. But if the ladies you are reviewing do not have much information on here, then a review might be helpful to other hobbyists.
I hope that my opinions here help guide you in your decision. A mod or more active hobbyist can tell you the current policy on getting review credit.