The targets that have been published are for ADMISSIONS into Canada, not ITAs, that's why last year, although the target admissions level was ~75000, by December they had issued a whopping 89,800 ITAs
(
https://www.cicnews.com/2018/12/can...core-to-lowest-of-2018-1211628.html#gs.987gkz)
People reject ITAs for all sorts of reasons, and people are rejected in their applications as well.
If just 10% of people who are issued ITAs either reject them or denied; your 80000 ITA target in reality becomes 88,888 actual ITAs being issued, which means using your logic
88,888 - 31250 = 57638 / 16 = 3602 ITAs every 2 weeks, an increase on the 3,350 number