I've already contacted shdvb about this and other cases.
I have asked also someone on last day about same issue. I don't think it's really necessary to send positive feedback's for every transaction. Is ther any difference with single positive feedback's and with 10 positive feedback's from same DT ? I don't think so, I am not sure if effect it on trust rating. But I think its better just left single feedback's if you want, especially for positive feedback's.
It allows for different references tho. Since it does not affect score you might as well document the different transactions.