PCC Mark Burns-Williamson said he was unaware the images existed until then.
He apologised for the "embarrassing" mistake but added: "There's been no intentional cover-up with this."
An employee at the PCC's office, who had previously been employed by the West Yorkshire Police Authority, remembered the storage device on 6 June 2017.
Taggart, who was a former police authority chairman, was jailed in July 2017 for making and distributing indecent photographs of children.
When officers had searched his home in September 2016 they discovered 36,003 indecent images and videos of children on his computer equipment.
A police whistleblower flagged up the hard drive's existence to the BBC in September 2017.
For full article https://www.bbc.co.uk/news/uk-england-leeds-51635721