I think attachment and transference are two different things. When I think of transference I think of feelings that I had toward my parents at one time, now being focused on t as though t was doing the kind of stuff my parents did.

Attachment I think happens all through life. Those that had healthy attachment as babies (or so the theory goes) can have healthy attachment to others as adults. Regardless of our history of attachment, we develop attachments of various kinds with other people in our lives not just (or mostly) with ts. For example I am attached to my husband, I love him, I like to be around him, I turn to him for comfort when things are bad, that sort of thing. I am attached to friends and family members and colleagues, all in different ways.

I think it gets confusing because some ts talk about transference as "part of the process" and "grist for the mill", and that will help you understand and work thru feelings toward parents. While others talk about attachment therapy, re-parenting and things like that that are supposed to help those who did not have healthy attachment as babies. I think you can have one without the other, though.