FYI The pyrite/cobalt and magnetite circuits were both...

FYI The pyrite/cobalt and magnetite circuits were both constructed and are essentially finished, all they need is cabling and for the scalped parts to be returned (they are essentially identical to the Copper circuit).

You are 100% correct that Cudeco knew the reserve was non-compliant as soon as they decided not to turn these circuits on. They admit it and claim they are working on an update back in September 2016 https://www.asx.com.au/asxpdf/20160922/pdf/43bcky3gy9ybdj.pdf

Page 2, small text “Note: The above indicative changes are provided as a guide only, and will be subject to change in an Ore Reserve Update”

So yes the question is why did it take them so long (exactly one year and six months) to revise and anounce it. The answer is probably because they intended to sweep it under the rug for as long as they could. From memory AMDAD didn’t even get started on it until the last quarter of 2017, at least a year after the announcement above.