Using named formulas, let the row of dates be
'dates' and the count
'n' refers to
= COLUMNS(dates)
The starting date of each period
'start' is one date short
= OFFSET( dates, 0, 0, 1, n-1 )
and the end date
'end' is offset one column to the right
= OFFSET( start, 0, 1 )
For a date to be valid, it must be a number, so
'validDate?' is the 'Boolean'
= ISNUMBER( start )
The key test for an error is provided by the Boolean
'outOforder?'
= (start>end)
Combining these into a single condition for conditional formatting
= OR( validDate? * outOfOrder? )
At this point I would tend to use a shape as a control to sort the range
Sometimes something more than text is called for if you are to get the attention of your users. This post suggests a way of introducing a button that colours or greys-out according to the situation.
www.spreadsheet1.com
but that would not work in the presence of the CANCELLED text.