Hi Anand,
You can display depreciation calculation in AW01N to get detail yearly depreciation calculation parameters, including segments created. If you're using new engine(EA-FIN ON), more than one segment may exist since many postings have been done.
About depreciation key setting, you can check period control rule for different postings then check the postings with their period control rule. Together with value in 'display depreciation calculation', I think you can get more information how depreciation is calculated.
Best regards,
Hannah