The Unswept Room - believability and autobiographical poetry

I have been reading a book of poetry by american poet Sharon Olds called The Unswept Room. The poems have a strong autobiographical flavour, many of them being about childhood and the author's relationship to her mother.

I found myself wondering this morning though how autobiograhical they actually are. It's interesting that when I read a poem I assume that it comes from experience but I know in my logical mind that this may not be the case. I have written poems that appear autobiographical; some of them are, some of them draw on my own experience but are embellished or played down, and some of them are entirely fictitious. The beauty of poetry is that you can create any persona or scenario you want to. So in some poems like Barabrith I have given the narrator a strong sense of history and ancestry:

but now, after all these years
full of black tea
and sticky brown sugar,
I think I know what it was that she meant.

and in others I have recounted incidents that might of happened like the argument in After the Party. Poetry gives the writer the opportunity to work through their difficult past events - to get them out of their system. The writer is able to acknowledge the past's power and and then stand it on its head and take its power away.

In Old's case some of the poems were so bleak (recounting incidents such as being tied to a chair as a child) that I almost wanted them NOT to be autobiographical. I suppose for me reading a poem is like watching a film or reading a noveL, I want to be able to believe in it while I am reading it. If it has a narrator I want to be able to believe in them and what they are saying and if I assume the poem is true then it means that the poem has succeeded in making me believe in it.