I disagree that the present definitions are clear . There are people who could fit into either T1 or T2 boxes and antibody and C peptide tests don't necessarily discriminate between the 2.
*Type 1
(beta-cell destruction, usually leading to absolute insulin deficiency)
1a Autoimmune
1b Idiopathic
by definition T1b encompasses the 10-15% percent of children and adults diagnosed with T1 who when tested have no autoimmune markers (ie we don't know it's cause.)
I'd note that an intermittent variety of T1b, found mainly in people of African or Asian descent. is specified as T1b in the official classification but is now often referred to as ketosis prone T2 . I'd also note tha new forms of idiopathic T1 have been described in the last few years.
eg fulminant T1 a very rapid onset T1 with no detectable antibodies.
*Type 2

redominantly insulin resistance with relative insulin deficiency or predominantly an insulin secretory defect with/without insulin resistance
That encompasses a very wide spectrum. The committee who devised the definition knew this
There are probably several different mechanisms which result in this form of diabetes, and it is likely that the number of people in this category will decrease in the future as identification of specific pathogenetic processes and genetic defects permits better differentiation and a more definitive classification with movement into "Other types".
The report says that by definition in T2
autoimmune destruction of the pancreas does not occur
Is it not possible that some of the people who fit in this rather large T2 box , those who are insulin deficient but not insulin resistant and are antibody negative actually have a slowly developing form of T1b ?
I've certainly ' met' some people like this online; lean, very low c peptide, insulin sensitve but no antibodies detected. Some have been diagnosed as T1, some as T2 it depends on the consultants clinical judgement.
I think it is also very likely that some groups of people in this category may have a form of genetic diabetes, like MODY which was once thought to be a form of T2 (hence the name)
* Definition, Diagnosis and Classification of Diabetes Mellitus and its Complications
http://www.staff.ncl.ac.uk/philip.home/who_dmc.htm